Application of Radiostereometric Analysis (RSA) to Triathlon Knee Components Inserted Using the OtisMed Custom-fit Total Knee Replacement System

Knee and hip arthroplasty are profoundly successful operative interventions, however, some joint replacements do fail and the life expectancy of a knee or hip arthroplasty is finite. This fact has largely been responsible for the continued development of new devices and techniques for joint arthroplasty surgery.

The OtisMed Custom-fit technique has great potential to shift knee replacement surgery to a more patient-specific paradigm. Existing studies with OtisMed surgeries have found a reduced need for soft-tissue releases, alignment comparable to conventional and computer navigated surgery, reduced tourniquet time, and reduced instrumentation. Although the preliminary results are promising the OtisMed Custom-fit system is still unproven, with no long-term follow-up studies completed to date. An initial report has questioned the effectiveness of the procedure although it is a very limited series of four surgeries. To definitively determine if the technique is an improvement on conventional knee arthroplasty a randomized controlled trial with high-resolution quantitative assessment of outcomes is clearly called for.

Question 1: Is there a difference in micromotion patterns for implant components between CAS and the OtisMed knee system?

• Null Hypothesis: There are no significant difference in micromotion patterns.
• Alternative Hypothesis: There are significant differences in micromotion patterns between the tibial and/or femoral components.

Question 2: Do the CAS knee components achieve adequate fixation to the underlying bone?

• Null Hypothesis: There is no significant continuous migration of the tibial and femoral components at 2 years indicating adequate long-term fixation at the implant - bone interface.
• Alternative Hypothesis: There is significant continuous migration of the tibial and/or femoral components at 2 years indicating inadequate fixation at the implant - bone interface.

Question 3: Do the OtisMed knee components achieve adequate fixation to the underlying bone?

• Null Hypothesis: There is no significant continuous migration of the tibial and femoral components at 2 years indicating adequate long-term fixation at the implant - bone interface.
• Alternative Hypothesis: There is significant continuous migration of the tibial and/or femoral components at 2 years indicating inadequate fixation at the implant - bone interface.

Question 4: For what proportion of implants in each group does migration continue to increase during the two year follow-up?

Question 5: Are inducible displacements, measured during loaded follow-up exams, different between the 2 groups?

Question 6: Are there significant differences in bone mineral density between the operative knee (proximal tibia) and other body sites over time?

Question 7: Are there significant differences in bone mineral density of the proximal tibia between the OtisMed and CAS groups over time?

Question 8: Is there a significant difference in gait symmetry measures, health status and functional outcome between the OtisMed and CAS groups?

Question 9: Is there a significant difference in postoperative full-leg length alignment between the CAS and OtisMed groups?

Question 10: Are there significant differences in the frontal plane alignment curves obtained from the CAS system between the CAS and OtisMed groups?

Question 12: Are there significant differences in the quantity of bone resection between the CAS and OtisMed groups?

Question 13: Are there significant differences in the frontal plane alignment curves obtained from the CAS system between the CAS and OtisMed groups?

Question 14: Are there significant differences in the number of intra-operative deviations from the surgical plan between the CAS and OtisMed groups?

Question 15: Is there a significant difference in the duration of surgery (tourniquet time) between the CAS and OtisMed groups?

Question 16: Is there a significant difference in the number of instrument pans used between the CAS and OtisMed groups?

Question 17: Is there a significant difference in length of hospital stay between the CAS and OtisMed groups?

Question 18: Are there intra-patient differences between the OtisMed surgical plan and the CAS surgical procedure in terms of predicted versus actual resection and alignment?

Inclusion criteria

• Symptomatic osteoarthritis of the knee indicating surgical intervention
• Between the ages of 21 and 80 inclusive
• Ability to give informed consent

Exclusion criteria

• Significant co-morbidity affecting ability to ambulate
• Flexion contracture greater than 15°
• Extension lag greater than 10°
• Tibial subluxation greater than 10 mm on standing AP radiograph
• Prior arthroplasty, patellectomy or osteotomy with the affected knee
• Lateral or medial collateral ligament instability (> 10° varus/valgus)
• Leg length discrepancy greater than 10 mm
• Pregnancy
• Active or prior infection
• Morbid Obesity (BMI > 40)
• Medical condition precluding major surgery
• Severe osteoporosis or osteopenia
• Neuromuscular impairment