Next Generation Personalized Restoration Technology :
The Bodycad Unicompartmental Knee System

The First Truly Patient Specific Implant Design

Introducing Bodycad’s revolutionary Unicompartmental Knee System, designed to optimize personalized restorations of the patient’s unique anatomical features and kinematics. The BUKS is based on proprietary 3D rendering of medical images of the patient’s anatomy. Recent studies of Unicompartmental Knee Arthroplasty (UKA) have demonstrated favorable outcomes, shorter hospital stays versus total knee arthroplasty, and lower 30-day readmissions.5, 6 In addition, there is clinical evidence that modest improvements in implant survivorship for younger patients will increase the cost-effectiveness of the treatment.7 The BUKS is designed to advance and improve upon this body of clinical evidence.

The BUKS Optimization

  • Designed to preserve bone and soft tissue
  • Minimizes bone loss
  • Includes instrumentation that is patient specific, intuitive and accurate
  • Provides an unconstrained design for a full range of motion
  • Engineered to fit the patient’s anatomy and kinematics
  • Has the potential for improved clinical results and patient satisfaction
  • Procedure in a box provides potentially greater efficiency and quality improvements to all stakeholders
  • Offers a unique and accurate resection solution which reduces issues related to saw blades

There's Nothing Standard About It

It Starts with Imaging

CT and MRI access, utility and reimbursement are growing in every country. Our proprietary imaging algorithms allow us to automatically and rapidly produce a precise 3D model of the knee. We have the capability to incorporate MRI, CT and long standing X-Ray data. CT and MRI data provides the best diagnostic information for surgeons. We also assist the surgeons and imaging centers by providing them with the Bodycad Unicompartmental Imaging Guide. Our required method of imaging for the BUKS is an MRI with a long standing coronal X-Ray.

  MRI Only MRI + Sagital Long Film Preferred
MRI + Coronal Long Film
MRI + Coronal & Sagittal Long Film Full Leg CT
Mechanical Axis Angle
Hip Knee Ankle Angle
Mechanical Axis Deviation
Varus Relative
Posterior Slope Relative
Example of BUK's Imaging Modalities and Measurements

Better Precision and Accuracy

The BUKS is designed with precision in mind. Evaluation of the precision and accuracy of implanting the BUKS tibial and femoral components in cadaver knees showed it to be the most precise of any current or traditional method. The Bodycad study reviewed 10 cadaver cases performed by three surgeons of varying levels of experience with UKA. Reported implant positioning accuracy results show that using conventional, robotic and navigated methods is not as accurate as Bodycad’s method on cadaveric models. 11, 12, 13, 14, 15

  Freehand Technique
(Cobb et al.2006)
Robotic Assistance
(Cobb et al.2006)
Robotic Assistance
(N.J.Dunbar et al.2012)
Bodycad Cadaveric Accuracy Study
Translation Error (mm) 2.2 1.1 1.3 0.9
Rotation Error (degrees) 5.5 2.4 2.4 2.2

Our proprietary, novel method of bone resection uses a patient-specific drill guide that provides for surgeon control of depth and accuracy. This reduces adverse issues associated with saw blade deflection, positional errors, and heat generation.16, 17, 18, 19, 20 One important factor in achieving precise placement of the BUKS is the provision for adjunctive fixation for both the tibial and femoral components. The final step in implanting the BUKS is securing the bone screws, which increases bone cement compression and insures complete and accurate seating in accordance with the surgical plan.

Clinical Outcomes for Personalized Arthroplasty

A personalized restoration has the potential for improved clinical results versus off-the-shelf products. A recent multi-center study of 120 custom UKA knees found improved range of motion, higher functional outcome scores, and lower pain scores. Patient satisfaction was high, with 99% of patients saying they were satisfied – 89% were very or extremely satisfied with the results of the procedure and 89% said the movement of the knee felt natural. Two years after surgery, only 2 patients had undergone revision for tibial loosening.1 In a quote from an orthopaedic surgeon’s in-press publication for The Journal of Arthroplasty, the following statement was made : “Patients really feel more stable with their custom knee replacements especially when they do activities like bending or walking down stairs which some patients with off-the-shelf knee replacements have difficulty with due to mid-flexion instability.” 2

Potential Quality and Economic Improvements for Personalized Arthroplasty

The potential for quality and economic improvements for personalized restorations versus off-the-shelf solutions has started to emerge in the clinical body of evidence. Reduced blood loss and swelling, decreased length of stay, and discharge optimization may lead to a better economic case for patient-specific solutions. One study concluded that the “differences in blood loss and swelling may be explained by the lack of femoral canal preparation and the ability to completely cover all cut bone surfaces in the customized TKR group.” 3 Another study documented a decrease of 1.1 days Length of Stay (LOS), a 36% increase in the 24hr discharge rate, and a higher percentage of patients discharged directly to home versus off-the-shelf solutions.4 These quality improvements should translate to considerable upgrades in episode of care efficiencies and cost effectiveness.

Anatomical Fit and Bone Preservation

The titanium tibial baseplate of the BUKS fits and covers the bone resection. It has recently been documented that a custom UKA provides significantly greater cortical rim surface area coverage compared to off-the-shelf implants: 77% versus 43% medially and 60% versus 37% laterally. In addition, significantly less cortical rim overhang and under coverage were measured.8 This increased coverage of resected bone may lead to decreased blood loss. The matching of the tibial baseplate to resected bone is inherent to the Bodycad design and manufacturing process, which translates into optimal coverage all of the time. The femoral component is also designed to match closely the anatomy of the patient’s femur. The femur is prepared by denuding the surface of cartilage and osteophytes, keeping bone removal to a minimum. This is important because studies have shown that a femoral component overhang of more than 3mm nearly doubles the odds of clinically important knee pain two years after total knee arthroplasty.9

Natural Kinematics

Bodycad’s solution is to re-establish the normal kinematics of the patient’s articulation by using a proprietary algorithm to best match the patient’s movement and anatomy. The Bodycad PREP Tech uses this information to develop an articulation specific to each patient. The results of one study postulate that knees with patient-specific implants generate kinematics more closely resembling normal knee kinematics than standard knee designs.10 Each and every Bodycad kinematic solution undergoes finite element analysis (FEA) to validate the design kinematics and contact stresses on the surface of the polyethylene insert. The polyethylene insert is available in 6mm to 10mm thicknesses in 1mm increments giving the surgeon flexibility for proper balancing of the knee

Efficient Surgical Work Flow and Lower Asset Intensity

A personalized arthroplasty greatly reduces inventory of instruments, eliminates implant inventory, and reduces costs of reprocessing instruments and unused implants because the delivery comes in a self-contained kit. This procedure in a box provides all the patient-specific instruments and implants. Traditional off-the-shelf products require a significant amount of asset intensity and human resources to ensure all components and instruments arrive on time into the operating room theatre, and instruments are cleaned and prepared for the next surgery. The reduction of asset intensity has the potential to increase the efficiency of the work flow in the hospital and operating theatre. These reductions may lead to improved cost benefits for all stakeholders. The BUKS kit is better suited for procedures performed in an out-patient surgery center, as well as for the bundled care approach, as it drives overall efficiency for the episode of care.

Procedure in a Box

Traditional Orthopaedics


  1. Barnes, CL, et al. “Customized, Individually Made Unicondylar Knee Replacement: A Prospective Multicenter Study of 2-Year Clinical Outcomes.” 2nd Annual Pan Pacific Orthopaedic Congress, Kona, Hawaii (July 22-25, 2015).
  2. “ConForMIS iTotal CR Outperformed Off the Shelf Implants.” Press Release (October 20th, 2016).
  3. Kurtz, et al. “Patient-Specific Knee Replacement Implants Preserve Bone and Decrease Blood Loss and Swelling.” BASK Annual Meeting, Poster Exhibit (2013).
  4. Buch, et al. “Clinical Study Presentation of an Independent, Prospective, Single-Center Investigator-Initiated Study of the iTotal CR Knee.” ICJR Pan Pacific Orthopaedic Congress (August 2016).
  5. Berger, Richard A., et al. “Results of Unicompartmental Knee Arthroplasty at a Minimum of Ten Years of Follow-Up.” The Journal of Bone & Joint Surgery - American Volume 87, 5 (May 2005): 999-1006.
  6. Drager, Jusin, et al. “Shorter Hospital Stay and Lower 30-Day Readmission after Unicondylar Knee Arthroplasty Compared to Total Knee Arthroplasty.” The Journal of Arthroplasty 31, 2 (February 2016): 356-361.
  7. Ghomrawi, Hassan, Ashley Eggman and Andrew D. Pearle. “Effect of Age on Cost-Effectiveness of Unicompartmental Knee Arthroplasty Compared with Total Knee Arthroplasty in the U.S.” The Journal of Bone & Joint Surgery - American Volume 97, 5 (March 2015): 396-402.
  8. Carpenter, Dylan P., et al. “Tibial Plateau Coverage in UKA: A Comparison of Patient Specific and Off-The-Shelf Implants.” The Journal of Arthroplasty 29, 9 (September 2014): 1694-1698.
  9. Mahoney, Ormonde M. and Tracy Kinsey. “Overhang of the Femoral Component in Total Knee Arthroplasty: Risk Factors and Clinical Consequences.” The Journal of Bone & Joint Surgery - American Volume 92, 5 (May 2010): 1115-1121.
  10. Patil, Shantanu, et al. “Patient -Specific Implants with Custom Cutting Blocks Better Approximate Natural Knee Kinematics than Standard TKA without Custom Cutting Blocks.” The Knee 22, 6 (August 2015).
  11. Internal Bodycad Test RAP-BP001-41, Bodycad UKS, “Prosthesis Position Accuracy Evaluation of Cadaver Specimen’s”. (December 2016).
  12. Karia, Monil, et al. “Robotic Assistance Enables Inexperienced Surgeons to Perform Unicompartmental Knee Arthroplasties on Dry Bone Models with Accuracy Superior to Conventional Methods.” Advances in Orthopedics vol. 2013.
  13. Cobb, J., et al. “Hands-On Robotic Unicompartmental Knee Replacement: A Prospective, Randomised Controlled Study of the Acrobot System.” The Bone & Joint Journal 88-B, 2 (February 2006): 188–197.
  14. Dunbar, Nicholas J., et al. “Accuracy of Dynamic Tactile-Guided Unicompartmental Knee Arthroplasty.” The Journal of Arthroplasty 27, 5 (May 2012): 803–808.e1.
  15. Smith, Julie R., Philip E. Riches and Philip J. Rowe. “Accuracy of a Freehand Sculpting Tool for Unicondylar Knee Replacement.” The International Journal of Medical Robotics and Computer Assisted Surgery 10, 2 (June 2014): 162-169.
  16. Goran, Augustin, et al. “Cortical Bone Drill and Thermal Osteonecrosis.” Clinical Biomechanics 27, 4 (May 2012): 313-325.
  17. Ohmori, Takaaki, et al. “The Accuracy of Initial Bone Cutting in Total Knee Arthroplasty.” Open Journal of Orthopaedics 5, 10 (October 2015): 297-304.
  18. Paskos, Christopher, et al. “Bone Cutting Errors in Total Knee Arthroplasty.” The Journal of Arthroplasty 17, 6 (September 2002): 698-705.
  19. Tawy,Gwenllian F., Philip J. Rowe, and Philip E. Riches. “Thermal Damage Done on Bone by Burring and Sawing With and Without Irrigation in Knee Arthroplasty.” The Journal of Arthroplasty 31, 5 (May 2016): 1102-1108.
  20. Toksvig-Larsen, Søren, Leif Ryd and Anders Lindstrand. “Temperature Influence in Different Orthopaedic Saw Blades.” The Journal of Arthroplasty 7, 1 (March 1992): 21-24.

BUKS Information

BUKS Brochure
BUKS Imaging Guide
Screw Fixation White Paper
Contact Stress Evaluation

Bodycad Unicompartmental Knee System library

Reusable Instruments

Bodycad Instrument Case

Bodycad Bone File

Bodycad Countersink Perforated Drill

Bodycad Cutting Pliers

Bodycad Explorer

Bodycad Extracting Forceps

Bodycad Femoral Impactor

Bodycad Hammer

Bodycad Osteotome 10mm

Bodycad Osteotome 15mm

Bodycad Peg Drill Bit

Bodycad Pin Punch

Bodycad Rongeur

Bodycad Round Open Curette 5mm

Bodycad Round Open Curved Curette 12mm

Bodycad Round Open Curved Curette 16mm

Bodycad Screwdriver

Bodycad Screwdriver Bit Torx T10

Bodycad Straigh Punch

Bodycad 3.5mm Drill Bit with Stop 65mm

Bodycad 3.5mm Drill Bit with Stop 75mm

Bodycad 3.5mm Drill Bit with Stop 90mm

Bodycad 3.5mm Drill Bit with Stop 100mm

Bodycad 3.5mm Drill Bit with Stop 110mm

Disposable Instruments

Bodycad Cut Explorer

Bodycad Cut Validator

Bodycad Extra Medullary Rod Support

Bodycad Femoral Cut Validator

Bodycad Femoral Cutting Guide

Bodycad Screw Caddy

Bodycad Tibial Baseplate Handle

Bodycad Tibial Cutting Guide

Bodycad Trial Insert


Bodycad BUKS

Bodycad Cemented Femoral Implant 1

Bodycad Cemented Femoral Implant 2

Bodycad Cemented Tibial Implant 1

Bodycad Cemented Tibial Implant 2

Bodycad Cemented Tibial Implant 3

Bodycad Femoral Component Fixation Screw

Bodycad Polythylene Locking Pin

Bodycad Retaining Screw for the Tibial and Femoral Cutting Guides

Bodycad Tibial Component Fixation Screw

Bodycad Tibial Insert


J Bone Joint Surg Am. 2003;85-A Suppl 4:115-22.
Anthropometric measurements of the human knee: correlation to the sizing of current knee arthroplasty systems. Hitt K1, Shurman JR 2nd, Greene K, McCarthy J, Moskal J, Hoeman T, Mont MA.

There is a paucity of data concerning the morphological dimensions of the distal part of the femur, the proximal part of the tibia, and the patella. The objective of this study was to analyze the exact anatomic data collected from a large group of patients undergoing total knee arthroplasty and to correlate the measurements to the dimensions of current prosthetic systems.
Eight different centers collected morphologic data from the distal part of the femur, the proximal part of the tibia, and the patella from 337 knees during total knee arthroplasty. Microcaliper measurements from templates and measuring guides were used to decrease intraobserver variation. The study included 188 women (209 knees) and 107 men (128 knees) who had a mean age of sixty-nine years. A characterization of the aspect ratio (the medial-lateral to anterior-posterior dimensions) was made for the proximal aspect of the tibia and the distal part of the femur. Known dimensions from six prosthetic knee systems were compared with the morphologic data.
A wide variation in the aspect ratio for the femoral component was seen among the six different prosthetic systems. For women, there was a significant association between the component size and the amount of medial-lateral overhang, with larger sizes having more overhang (p < 0.0001). Although the femoral aspect ratio for the morphologic data showed higher ratios for smaller knees and proportionally lower ratios for larger knees, the designs showed little change in the aspect ratio. The tibial aspect ratio from the morphologic data showed a higher ratio for smaller knees and a proportionally lower ratio for larger knees. The Duracon component tracked the decline in aspect ratio fairly well, whereas the other brands either did not change with anterior-posterior dimension or actually increased (NexGen). Gender differences in the morphologic data were shown by the variable tibial aspect ratios. A comparison of the bone dimensions from the study data and the dimensions of the implants indicated that the smaller sizes were too small while the larger sizes tended to be too large. The average overall unresected patellar thickness was 23.7 mm.
The results of this study will allow manufacturers to make more appropriate determinations of the sizes and aspect ratios of components for use in total knee arthroplasty

J Arthroplasty. 2015 Aug;30(8):1434-8. doi: 10.1016/j.arth.2015.02.027. Epub 2015 Feb 28.
Important Differences Exist in Posterior Condylar Offsets in an Osteological Collection of 1,058 Femurs. Weinberg DS1, Streit JJ1, Gebhart JJ1, Williamson DF1, Goldberg VM1.

Posterior condylar offset (PCO) has important implications in total knee arthroplasty (TKA) function and design. In an osteological study of 1,058 femurs, we measured PCO using two separate techniques with a 3D digitizer. Measurements were standardized for the size of the femur. The medial PCO was greater than lateral PCO (32.6mm vs. 31.2mm, P<0.0001). in 53% of individuals, the medial pco differed between sides by more than 2mm. age did not affect standardized medial or lateral pco. compared with african-americans, caucasians had a larger standardized medial (1.3mm vs. 1.2mm, p=0.006) and lateral (1.1mm vs. 1.0mm, p=0.004) pcos. the standardized medial (1.2mm vs. 1.3mm, p=0.073), and lateral (1.1mm vs. 1.1mm, p=0.098), pco did not differ between men and women, respectively.

J Arthroplasty. 1992 Mar;7(1):21-4.
Temperature influence in different orthopaedic saw blades. Toksvig-Larsen S1, Ryd L, Lindstrand A.

Laboratory tests were carried out on ox bone to evaluate the thermal effect of eight different saw blades while cutting cortical bone. These saw blades represented the usual clinical blades as well as saw blades specially manufactured in an attempt to decrease the temperature. Temperatures between 34 degrees C and 450 degrees C were registered in the saw blades. Only three measurements (of 219 tests) were below 44 degrees-47 degrees C, which is a critical limit for heat-induced bone necrosis. This test indicates that alternating saw blade design is not a way to control the temperature elevation during cutting of bone in orthopaedic procedures

Open Journal of Orthopedics 2015, 5, 297-304
The Accuracy of Initial Bone Cutting in Total Knee Arthroplasty. Takaaki Ohmori, Toru Maeda, Tamon Kabata, Yoshitomo Kajino, Shintaro Iwai, Hiroyuki Tsuchiya

Background: The aim of this study was to evaluate the accuracy of initial bone cutting of the distal femur and the proximal tibia in TKA using an image-free navigation system. Methods: From February 2006 to March 2013, we evaluated 60 knees in 50 patients using an image-free navigation system (Navigation: Stryker Navigation Cart System; Software: Stryker Knee Navigation; Ver2.0: Stryker Orthopaedics US NJ Mahwah). First, we measured the angle shown by the navigation system before cutting, at the time we set the jig. Second, we measured the angles shown by navigation after the bone was cut using the jig. Then, we compared these two angles for each patient to determine the bone cutting error. Results: In the distal femur, 37 of 60 knees were cut in an extended position in the sagittal plane, and 26 of 60 knees were cut in a varus in the coronal plane. In the proximal tibia, 29 of 60 knees were cut with decreased posterior slope in the sagittal plane, and 26 of 60 knees were cut in a valgus. Conclusions: In this study, the distal femur tended to be cut in an extended and a varus position and the proximal tibia did with decreased posterior slope and in a valgus position after initial bone cutting. It is necessary to note the initial cutting error in TKA. Since cutting errors affect postoperative outcome, we should cut bones several times. And as the reasons of the cause of the error, we propose new reason that cutting bone is not parallel with accuracy to AP axis.

J Arthroplasty. 2002 Sep;17(6):698-705.
Bone cutting errors in total knee arthroplasty. Plaskos C, Hodgson AJ, Inkpen K, McGraw RW.

Although achieving precise implant alignment is crucial for producing good outcomes in total knee arthroplasty, the contribution of the bone-cutting process to overall variability has not been measured previously. Eight orthopaedic surgeons with varying amounts of total knee arthroplasty experience performed 85 resections on 19 cadaver femora and tibiae, and the planes of the resulting cut surfaces were compared with the guide planes. Varus-valgus alignment variability ranged from 0.4 degrees to 0.8 degrees SD for expert and trainee surgeons. Sagittal variability was approximately 1.3 degrees SD for both surgeon groups. Slotted cutting guides reduced the variability and eliminated the bias in the sagittal plane for experienced surgeons but did not improve significantly frontal plane alignment variability. Guide movement contributed 10% to 40% of the total cutting error, depending on cut and guide type.

J Bone Joint Surg Br. 2009 Jan;91(1):52-7. doi: 10.1302/0301-620X.91B1.20899.
Unicompartmental or total knee replacement: the 15-year results of a prospective randomised controlled trial. Newman J, Pydisetty RV, Ackroyd C.

Background: The aim of this study was to evaluate the accuracy of initial bone cutting of the distal femur and the proximal tibia in TKA using an image-free navigation system. Methods: From February 2006 to March 2013, we evaluated 60 knees in 50 patients using an image-free navigation system (Navigation: Stryker Navigation Cart System; Software: Stryker Knee Navigation; Ver2.0: Stryker Orthopaedics US NJ Mahwah). First, we measured the angle shown by the navigation system before cutting, at the time we set the jig. Second, we measured the angles shown by navigation after the bone was cut using the jig. Then, we compared these two angles for each patient to determine the bone cutting error. Results: In the distal femur, 37 of 60 knees were cut in an extended position in the sagittal plane, and 26 of 60 knees were cut in a varus in the coronal plane. In the proximal tibia, 29 of 60 knees were cut with decreased posterior slope in the sagittal plane, and 26 of 60 knees were cut in a valgus. Conclusions: In this study, the distal femur tended to be cut in an extended and a varus position and the proximal tibia did with decreased posterior slope and in a valgus position after initial bone cutting. It is necessary to note the initial cutting error in TKA. Since cutting errors affect postoperative outcome, we should cut bones several times. And as the reasons of the cause of the error, we propose new reason that cutting bone is not parallel with accuracy to AP axis.

J Bone Joint Surg Am. 2005 May;87(5):999-1006.
Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up. Berger RA, Meneghini RM, Jacobs JJ, Sheinkop MB, Della Valle CJ, Rosenberg AG, Galante JO.

There is a renewed interest in unicompartmental knee arthroplasty. The present report describes the minimum ten-year results associated with a unicompartmental knee arthroplasty design that is in current use.
Sixty-two consecutive unicompartmental knee arthroplasties that were performed with cemented modular Miller-Galante implants in fifty-one patients were studied prospectively both clinically and radiographically. All patients had isolated unicompartmental disease without patellofemoral symptoms. No patient was lost to follow-up. Thirteen patients (thirteen knees) died after less than ten years of follow-up, leaving thirty-eight patients (forty-nine knees) with a minimum of ten years of follow-up. The average duration of follow-up was twelve years.
The mean Hospital for Special Surgery knee score improved from 55 points preoperatively to 92 points at the time of the final follow-up. Thirty-nine knees (80%) had an excellent result, six (12%) had a good result, and four (8%) had a fair result. At the time of the final follow-up, thirty-nine knees (80%) had flexion to at least 120 degrees . Two patients (two knees) with well-fixed components underwent revision to total knee arthroplasty, at seven and eleven years, because of progression of patellofemoral arthritis. At the time of the final follow-up, no component was loose radiographically and there was no evidence of periprosthetic osteolysis. Radiographic evidence of progressive loss of joint space was observed in the opposite compartment of nine knees (18%) and in the patellofemoral space of seven knees (14%). Kaplan-Meier analysis revealed a survival rate of 98.0% +/- 2.0% at ten years and of 95.7% +/- 4.3% at thirteen years, with revision or radiographic loosening as the end point. The survival rate was 100% at thirteen years with aseptic loosening as the end point.
After a minimum duration of follow-up of ten years, this cemented modular unicompartmental knee design was associated with excellent clinical and radiographic results. Although the ten-year survival rate was excellent, radiographic signs of progression of osteoarthritis in the other compartments continued at a slow rate. With appropriate indications and technique, this unicompartmental knee design can yield excellent results into the beginning of the second decade of use.

J Bone Joint Surg Am. 2015 Mar 4;97(5):396-402. doi: 10.2106/JBJS.N.00169.
Effect of age on cost-effectiveness of unicompartmental knee arthroplasty compared with total knee arthroplasty in the U.S. Ghomrawi HM, Eggman AA, Pearle AD.

Trade-offs between upfront benefits and later risk of revision of unicompartmental knee arthroplasty compared with those of total knee arthroplasty are poorly understood. The purpose of our study was to compare the cost-effectiveness of unicompartmental knee arthroplasty with that of total knee arthroplasty across the age spectrum of patients undergoing knee replacement.
Using a Markov decision analytic model, we compared unicompartmental knee arthroplasty with total knee arthroplasty with regard to lifetime costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs) from a societal perspective for patients undergoing surgery at forty-five, fifty-five, sixty-five, seventy-five, or eighty-five years of age. Transition probabilities were estimated from the literature; survival, from the Swedish Knee Arthroplasty Register; and costs, from the literature and the Healthcare Cost and Utilization Project (HCUP) database. Costs and QALYs were discounted at 3.0% annually. We conducted sensitivity analyses to test the robustness of model estimates and threshold analyses.
For patients sixty-five years of age and older, unicompartmental knee arthroplasty dominated total knee arthroplasty, with lower lifetime costs and higher QALYs. Unicompartmental knee arthroplasty was no longer cost-effective at a $100,000/QALY threshold when total knee arthroplasty rehabilitation costs were reduced by two-thirds or more for these older patients. Lifetime societal savings from utilizing unicompartmental knee arthroplasty in all older patients (sixty-five or older) in 2015 and 2020 were $56 to $336 million and $84 to $544 million, respectively. In the forty-five and fifty-five-year-old age cohorts, total knee arthroplasty had an ICER of $30,300/QALY and $63,000/QALY, respectively. Unicompartmental knee arthroplasty became cost-effective when its twenty-year revision rate dropped from 27.8% to 25.7% for the forty-five-year age group and from 27.9% to 26.7% for the fifty-five-year age group.
Unicompartmental knee arthroplasty is an economically attractive alternative in patients sixty-five years of age or older, and modest improvements in implant survivorship could make it a cost-effective alternative in younger patients.

J Arthroplasty. 2015 Sep 18. pii: S0883-5403(15)00828-1. doi: 10.1016/j.arth.2015.09.014. [Epub ahead of print]
Shorter Hospital Stay and Lower 30-Day Readmission After Unicondylar Knee Arthroplasty Compared to Total Knee Arthroplasty. Drager J, Hart A, Khalil JA, Zukor DJ, Bergeron SG, Antoniou J.

Reducing hospital stay and unplanned hospital readmission of arthroplasty patients has been a topic of recent interest. The aim of the present study was to query the National Surgical Quality Improvement Program database to compare the length of hospital stay (LOS) and the subsequent 30-day hospital readmission rates in patients undergoing primary unicondylar knee arthroplasty (UKA) and total knee arthroplasty (TKA).
We identified 1340 UKAs and 36,274 TKAs over a 2-year period (2011-2012). Patient demographics, comorbidities, LOS, 30-day postoperative complications, and readmission rates were compared between the groups. Multivariate regression analysis was used to determine the effect of procedure type on LOS and readmission rates.
Unicondylar knee arthroplasty patients had a median LOS of 2 days compared to 3 days for TKAs (P < .001). The readmission rate in the TKA group was nearly double that of the UKA group (4.1% vs 2.2%) (P < .0001). Multivariate regression analysis identified that undergoing a UKA was predictive for a shorter LOS (coefficient -1 day) and was protective for 30-day readmission (odds ratio, 0.60; 95% confidence interval, 0.41-0.88).
Patients undergoing UKA had a shorter LOS and a lower 30-day readmission rate compared to TKA patients. After adjusting for selected cofounders, we demonstrated that undergoing a UKA is a protective factor for 30-day readmission.
Copyright © 2015 Elsevier Inc. All rights reserved.

J Arthroplasty. 2013 Oct;28(9 Suppl):176-8. doi: 10.1016/j.arth.2013.07.036.
Unicompartmental knee arthroplasty enables near normal gait at higher speeds, unlike total knee arthroplasty. Wiik AV, Manning V, Strachan RK, Amis AA, Cobb JP.

Top walking speed (TWS) was used to compare UKA with TKA. Two groups of 23 patients, well matched for age, gender, height and weight and radiological severity were recruited based on high functional scores, more than twelve months post UKA or TKA. These were compared with 14 preop patients and 14 normal controls. Their gait was measured at increasing speeds on a treadmill instrumented with force plates. Both arthroplasty groups were significantly faster than the preop OA group. TKA patients walked substantially faster than any previously reported series of knee arthroplasties. UKA patients walked 10% faster than TKA, although not as fast as the normal controls. Stride length was 5% greater and stance time 7% shorter following UKA - both much closer to normal than TKA. Unlike TKA, UKA enables a near normal gait one year after surgery.

J Biomech 2005 Feb;38(2):269-76.
Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using 'interventional' MRI. Johal P, Williams A, Wragg P, Hunt D, Gedroyc W.

The aim of this study was to image tibio-femoral movement during flexion in the living knee. Ten loaded male Caucasian knees were initially studied using MRI, and the relative tibio-femoral motions, through the full flexion arc in neutral tibial rotation, were measured. On knee flexion from hyperextension to 120 degrees , the lateral femoral condyle moved posteriorly 22 mm. From 120 degrees to full squatting there was another 10 mm of posterior translation, with the lateral femoral condyle appearing almost to sublux posteriorly. The medial femoral condyle demonstrated minimal posterior translation until 120 degrees . Thereafter, it moved 9 mm posteriorly to lie on the superior surface of the medial meniscal posterior horn. Thus, during flexion of the knee to 120 degrees , the femur rotated externally through an angle of 20 degrees . However, on flexion beyond 120 degrees , both femoral condyles moved posteriorly to a similar degree. The second part of this study investigated the effect of gender, side, load and longitudinal rotation. The pattern of relative tibio-femoral movement during knee flexion appears to be independent of gender and side. Femoral external rotation (or tibial internal rotation) occurs with knee flexion under loaded and unloaded conditions, but the magnitude of rotation is greater and occurs earlier on weight bearing. With flexion plus tibial internal rotation, the pattern of movement follows that in neutral. With flexion in tibial external rotation, the lateral femoral condyle adopts a more anterior position relative to the tibia and, particularly in the non-weight bearing knee, much of the femoral external rotation that occurs with flexion is reversed.

The Knee (Impact Factor: 1.94). 08/2015; DOI: 10.1016/j.knee.2015.08.002
Patient-specific implants with custom cutting blocks better approximate natural knee kinematics than standard TKA without custom cutting blocks. Patil, Shantanu, Adam Bunn, William D. Bugbee, Clifford W. Colwell, and Darryl D. D’Lima

Nearly 14% to 39% TKA patients report dissatisfaction causing incomplete return of function. We proposed that the kinematics of knees implanted with patient-specific prostheses using patient-specific cutting guides would be closer to normal.
Eighteen matched cadaver lower limbs were randomly assigned to two groups: group A was implanted with patient-specific implants using patient-specific cutting guides; group B, the contralateral knee, was implanted with a standard design using intramedullary alignment cutting guides. Knee kinematics were measured on a dynamic closed-kinetic-chain Oxford knee rig, simulating a deep knee bend and in a passive rig testing varus-valgus laxity.
The difference from normal kinematics was lower for group A compared to group B for active femoral rollback, active tibiofemoral adduction, and for passive varus-valgus laxity.
Our results support the hypothesis that knees with patient-specific implants generate kinematics more closely resembling normal knee kinematics than standard knee designs.
Clinical Relevance:
Restoring normal kinematics may improve function and patient satisfaction after total knee arthroplasty

J Arthroplasty. 2012 Sep;27(8 Suppl):86-90. doi: 10.1016/j.arth.2012.03.022. Epub 2012 May 4.
Total knee arthroplasty has higher postoperative morbidity than unicompartmental knee arthroplasty: a multicenter analysis. Brown NM, Sheth NP, Davis K, Berend ME, Lombardi AV, Berend KR, Della Valle CJ.

A total of 2235 primary total knee arthroplasties (TKAs) and 605 unicompartmental knee arthroplasties performed at 3 institutions over 5 years were reviewed to compare the incidence of postoperative complications between these groups. The overall risk of complications for patients undergoing TKA was 11.0%, compared with 4.3% for patients undergoing unicompartmental knee arthroplasty (P < .0001). Total knee arthroplasty was associated with increased rates of manipulation (odds ratio [OR], 13.0; P < .0001), transfusion (OR, 8.5; P = .036), intensive care unit admission (OR, 7.4; P = .049), discharge to a rehabilitation facility (OR, 5.2; P < .0001) and had longer hospital stays (mean, 3.3 vs 2.0 days; P < .0001). There was a trend toward an increased risk of deep infection (0.8% vs 0.2%, P = .13), readmission (4.2% vs 2.7%, P = .0795), thromboembolic events (1.0% vs 0.64%, P = .398), and any reoperation (1.4% vs 0.6%; P = .064). The increased risk of perioperative complications after TKA should be considered when counseling patients if they are an appropriate candidate for either procedure.

Int Orthop. 2014 Feb;38(2):443-7. doi: 10.1007/s00264-013-2214-9. Epub 2013 Dec 13.
Feasibility and safety of performing outpatient unicompartmental knee arthroplasty. Cross MB, Berger R.

Unicompartmental knee arthroplasty (UKA) has a faster short-term recovery than total knee arthroplasty (TKA). The purpose of this study was to determine the feasibility and safety of performing outpatient UKAs in a consecutive group of patients presenting with unicompartmental knee osteoarthritis.
A total of 105 consecutive patients underwent unicompartmental arthroplasty before noon with the intention of being discharged as an outpatient. All patients followed an established rapid recovery pathway to facilitate a same-day discharge. Post-operative complications and hospital readmissions were retrospectively recorded for all patients at one week and at three months after surgery.
All of the 105 patients (100 %) indicated for outpatient UKA could be discharged home on the same day of surgery. No patients required readmission within the first week post-operatively, while one patient required readmission between week one and week 12. The single patient who required readmission developed a post-operative infection requiring irrigation/debridement with polyethylene liner exchange and intravenous antibiotics.
Using an established, multidisciplinary, rapid recovery protocol, outpatient UKA is safe and feasible in the vast majority of patients.

J Bone Joint Surg Am. 2010 Dec 15;92(18):2890-7. doi: 10.2106/JBJS.I.00917.
Pain and function in patients after primary unicompartmental and total knee arthroplasty. Lygre SH, Espehaug B, Havelin LI, Furnes O, Vollset SE.

Unicompartmental knee arthroplasty has received renewed interest; however, its short-term advantages over total knee arthroplasty should be weighed against a higher risk of reoperation. Information regarding pain and function after unicompartmental and total knee arthroplasty is therefore needed.
Patient-reported data regarding pain and function were collected, at least two years postoperatively and by way of postal questionnaire, from 1344 patients who were listed on the Norwegian Arthroplasty Register as having had an unrevised primary total knee arthroplasty (972 patients) or a unicompartmental knee arthroplasty (372 patients) for the treatment of arthritis. Outcomes were assessed (with a score of zero indicating the worst possible outcome and a score of 100 indicating the best possible outcome) with use of the five subscales from the Knee Injury and Osteoarthritis Outcome Score, the scores from visual analog scales regarding degree of pain and satisfaction with the surgery, and the change in index score (from preoperative to postoperative) on the EuroQol-5D health-related quality-of-life instrument. We also used all forty-two questions from the Knee Injury and Osteoarthritis Outcome Score as outcome measures. To be regarded as clinically significant, the differences needed to be eight units for the Knee Injury and Osteoarthritis Outcome Score outcomes, ten units for the pain and satisfaction scales, and 0.4 unit for the detailed Knee Injury and Osteoarthritis Outcome Score questions.
Unicompartmental knee implants performed better than total knee implants on the Knee Injury and Osteoarthritis Outcome subscales for "Symptoms" (adjusted mean difference, 2.7; p = 0.04), "Function in Daily Living" (adjusted mean difference, 4.1; p = 0.01), and "Function in Sport and Recreation" (adjusted mean difference, 5.4; p = 0.006). Of the forty-two analyses of the detailed questions, four differences were significant. These differences were in favor of unicompartmental knee arthroplasty, but only the question "Can you bend your knee fully?" reached the level of clinical significance.
We found only small or no differences in pain and function between the scores, at least two years following surgery, of patients who underwent unicompartmental knee arthroplasty and those of patients who underwent total knee arthroplasty; however, patients with unicompartmental knee implants had fewer problems with activities that involved bending the knee

J Bone Joint Surg Am. 2010 May;92(5):1115-21. doi: 10.2106/JBJS.H.00434.
Overhang of the femoral component in total knee arthroplasty: risk factors and clinical consequences. Mahoney OM, Kinsey T.

Recently, much attention has been directed to femoral component overhang in total knee arthroplasty. The purposes of this study were to describe the prevalence of femoral component overhang among men and women after total knee arthroplasty, to identify risk factors for overhang, and to determine whether overhang was associated with postoperative knee pain or decreased range of motion.
Femoral component overhang was measured intraoperatively during 437 implantations of the same type of total knee arthroplasty prosthesis. The overhang of metal beyond the bone cut edge was measured in millimeters at the midpoint of ten zones after permanent fixation of the implant. Factors predictive of overhanging fit were identified, and the effect of overhang on postoperative pain and flexion was examined.
Overhang of >or=3 mm occurred in at least one zone among 40% (seventy-one) of 176 knees in men and 68% (177) of 261 knees in women, most frequently in lateral zones 2 (anterior-distal) and 3 (distal). Female sex, shorter height, and larger femoral component size were highly predictive of greater overhang in multivariate models. Femoral component overhang of >or=3 mm in at least one zone was associated with an almost twofold increased risk of knee pain more severe than occasional or mild at two years after surgery (odds ratio, 1.9; 95% confidence interval, 1.1 to 3.3).
In this series, overhang of the femoral component was highly prevalent, occurring more often and with greater severity in women, and the prevalence and magnitude of overhang increased with larger femoral component sizes among both sexes. Femoral component overhang of >or=3 mm approximately doubles the odds of clinically important knee pain two years after total knee arthroplasty

J Arthroplasty. 2014 Sep;29(9):1694-8. doi: 10.1016/j.arth.2014.03.026. Epub 2014 Mar 28.
Tibial plateau coverage in UKA: a comparison of patient specific and off-the-shelf implants. Carpenter DP, Holmberg RR, Quartulli MJ, Barnes CL.

Poor tibial component fit can lead to issues including pain, loosening and subsidence. Morphometric data, from 30 patients undergoing UKA were utilized; comparing size, match and fit between patient-specific and off-the-shelf implants. CT images were prospectively obtained and implants modeled in CAD, utilizing sizing templates with off-the-shelf and CAD designs with patient-specific implants. Virtual surgery was performed, maximizing tibial plateau coverage while minimizing implant overhang. Each implant evaluated to examine tibial fit. Patient-specific implants provided significantly greater cortical rim surface area coverage versus off-the-shelf implants: 77% v. 43% medially and 60% v. 37% laterally. Significantly less cortical rim overhang and undercoverage were observed with patient-specific implants. Patient-specific implants provide superior cortical bone coverage and fit while minimizing overhang and undercoverage seen in off-the-shelf implants.

J Bone Joint Surg Am. 2003 Mar;85-A(3):464-8
Effect of terminal sterilization with gas plasma or gamma radiation on wear of polyethylene liners. Hopper RH Jr, Young AM, Orishimo KF, Engh CA Jr.

Although terminal sterilization with gamma radiation in air promotes cross-linking, which improves wear resistance, it also results in free radicals, which can oxidize and degrade the mechanical properties of polyethylene liners used for total hip arthroplasty. For this reason, non-cross-linked polyethylene components have also been sterilized with chemical surface treatments, such as gas plasma. In this study, we tested the hypothesis that conventional polyethylene liners cross-linked by sterilization with gamma radiation in air had better in vivo wear performance than non-cross-linked liners sterilized with gas plasma.
We retrospectively reviewed the wear rates in a series of hips treated with a Duraloc 100 cup, a 28-mm femoral head, and an Enduron liner that had been sterilized with either gamma radiation (sixty-one hips followed for a mean of 5.2 years) or gas plasma (sixty-three hips followed for a mean of 3.9 years). The irradiated liners had been stored with access to ambient oxygen for an average of 1.0 year (range, 0.05 to 5.72 years) prior to implantation. Multiple linear regression was used to assess the effect of the sterilization method on the wear rate while accounting for the possible influence of other factors, including liner geometry, femoral head material, patient gender, cup abduction angle, and age at surgery.
The polyethylene liners that had been sterilized with gamma radiation in air had a significantly lower wear rate than did the gas-plasma-sterilized liners (0.097 compared with 0.19 mm/yr, p < 0.001). The sterilization method (p < 0.001) and age at surgery (p = 0.001) were the only factors that we analyzed that correlated with the wear rate.
The in vivo wear of conventional polyethylene liners that had been sterilized with gamma radiation in air was, on the average, 50% less than that of non-cross-linked liners sterilized with gas plasma.

J Bone Joint Surg Am. 2009 Apr;91(4):839-49. doi: 10.2106/JBJS.H.00538.
Gamma inert sterilization: a solution to polyethylene oxidation? Medel FJ, Kurtz SM, Hozack WJ, Parvizi J, Purtill JJ, Sharkey PF, MacDonald D, Kraay MJ, Goldberg V, Rimnac CM.

In the 1990s, oxidation was found to occur in ultra-high molecular weight polyethylene total joint replacement components following gamma irradiation and prolonged shelf aging in air. Orthopaedic manufacturers developed barrier packaging to reduce oxidation during and after radiation sterilization. The present study explores the hypothesis that polyethylene components sterilized in a low-oxygen environment undergo similar in vivo oxidative mechanisms as inserts sterilized in air. In addition, the potential influence of the different sterilization processes on the wear performance of the polyethylene components was examined.
An analysis of oxidation, wear, and surface damage was performed for forty-eight acetabular liners and 123 tibial inserts. The mean implantation time was 12.3+/-3.7 years for thirty-one acetabular liners that had been gamma sterilized in air and 4.0+/-2.5 years for the seventeen acetabular liners that had been gamma sterilized in inert gas. The mean implantation time was 11.0+/-3.2 years for the twenty-six tibial inserts that had been sterilized in air and 2.8+/-2.2 years for the ninety-seven tibial inserts that had been gamma sterilized in inert gas. Oxidation and hydroperoxide levels were characterized in loaded and unloaded regions of the inserts.
Measurable oxidation and oxidation potential were observed in all cohorts. The oxidation and hydroperoxide levels were regional. Surfaces with access to body fluids were more heavily oxidized than protected bearing surfaces were. This variation appeared to be greater in historical (gamma-in-air-sterilized) components. Regarding wear performance, historical and conventional acetabular liners showed similar wear penetration rates, whereas a low incidence of delamination was confirmed for the conventional tibial inserts in the first decade of implantation.
The present study explores the impact of industry-wide changes in sterilization practices for polyethylene. We found lower oxidation and oxidation potential in the conventional acetabular liners and tibial inserts that had been gamma sterilized in inert gas as compared with the historical components that had been gamma sterilized in air. However, we also found strong evidence that conventional components undergo mechanisms of in vivo oxidation similar to those observed following gamma irradiation in air. In addition, gamma sterilization in inert gas did not provide polyethylene with a significant improvement in terms of wear resistance as compared with gamma sterilization in air, except for a lower incidence of delamination in the first decade of implantation for tibial inserts

Clin Orthop Relat Res. 2013 Jan;471(1):181-8. doi: 10.1007/s11999-012-2505-2.
The ACL in the arthritic knee: how often is it present and can preoperative tests predict its presence? Johnson AJ, Howell SM, Costa CR, Mont MA.

TKA with retention of the anterior cruciate ligament (ACL) may improve kinematics and function. However, conflicting reports exist concerning the prevalence of intact ACLs at the time of TKA.
Therefore, we asked: (1) what was the ACL status at TKA; (2) what was the sensitivity and specificity of the Lachman test; (3) did MRI ACL integrity correlate with intraoperative observation; (4) did MRI tibial wear patterns correlate with ACL integrity; and (5) did ACL status depend on age or sex?
We evaluated 200 patients for ACL integrity at the time of TKA. All patients underwent a Lachman test under anesthesia. Intraoperatively, the ACL was characterized as intact, frayed, disrupted, or absent. In 100 patients, MRIs were performed, from which the ACL was graded as intact, indeterminate, or disrupted, and the AP location of tibial wear was categorized.
The ACL was intact in 155 patients (78%). The Lachman test alone had poor diagnostic ability. The MRI predicted a tear, but we observed two ACLs with indeterminate status that were disrupted. All knees with anterior wear on the medial tibial condyle had an intact ACL (n = 45), and all knees with posterior wear on the medial tibial condyle had a disrupted ACL (n = 8).
Although the Lachman test alone had poor sensitivity, when combined with MRI they together provide a sensitivity of 93.3% and specificity of 99%, which we believe makes these reasonable tests for assessing ACL status in the arthritic knee.

J Bone Joint Surg Am. 2003 Oct;85-A(10):1968-73.
Unicompartmental knee arthroplasty in patients sixty years of age or younger. Pennington DW, Swienckowski JJ, Lutes WB, Drake GN.

Unicompartmental knee arthroplasty has been used to treat elderly, low-demand patients, but the literature is sparse regarding the use of this procedure for younger, active patients. The purpose of the present retrospective study was to evaluate the results of unicompartmental knee arthroplasty in younger, more active patients.
Forty-one patients underwent forty-six consecutive unicompartmental knee arthroplasties with use of the Miller-Galante system between 1988 and 1996. All of the patients were sixty years of age or younger and all were physically active. The Hospital for Special Surgery knee score and the University of California at Los Angeles activity assessment were used to rate the function and to determine the activity level of each patient, respectively. Serial radiographs were used to evaluate the status of prosthetic fixation, femorotibial alignment, and the progression of arthrosis in the unreplaced compartment. Long-term survivorship was calculated with use of Kaplan-Meier analysis.
The mean duration of follow-up was eleven years. Of the forty-five knees that were available for follow-up, three had been revised. The Hospital for Special Surgery score was excellent for thirty-nine (93%) of the remaining forty-two knees and good for three. The University of California at Los Angeles activity assessment score was 6.6 +/- 1.4 for the knees in which the original prosthesis had been retained and 7.3 +/- 1.5 for those in which it had been revised. Two asymptomatic patients had revision of a modular tibial component because of substantial radiographic evidence of polyethylene wear; one of these patients had exchange of the polyethylene insert and the tibial tray, and the other had exchange of the polyethylene insert only. A third patient underwent revision total knee arthroplasty because of continuing knee pain and a progressive tibial radiolucent line that was >2 mm in width. The average postoperative femorotibial alignment was 5 degrees of valgus. Nine knees had progression of arthritis in the unresurfaced compartment; none of these knees were revised, and none of the patients had deterioration in the Hospital for Special Surgery score. Kaplan-Meier analysis demonstrated an eleven-year survivorship of 92%.
At an average duration of follow-up of eleven years, unicompartmental knee arthroplasty was associated with pain relief and excellent function in a cohort of patients who had been sixty years of age or younger and active at the time of surgery.

It's only a matter of time before personalized restorations become the better option for many orthopedic surgeons. Improved implant design and surgical technique of the Bodycad Unicompartmental Knee are defining a new standard in knee replacement surgery.

-Dr. Nicolas Duval