Advanced Bilateral Knee Osteoarthritis: A Comprehensive Clinical Case Study
Key Takeaway
Severe knee osteoarthritis diagnosis involves assessing patient history for chronic pain exacerbated by activity, morning stiffness, and failed conservative treatments. Physical exam reveals varus deformity, fixed flexion, restricted ROM, and often ligamentous laxity. Imaging like standing AP radiographs confirm severe joint space narrowing, osteophytes, subchondral sclerosis, and Kellgren-Lawrence Grade IV changes.
You are presented with a 68-year-old retired carpenter complaining of 7 years of progressive right knee pain. He has failed conservative management including NSAIDs and multiple injections. On examination, he has a fixed flexion deformity of 10 degrees and a significant varus deformity with >10mm opening on varus stress testing at 30 degrees of flexion. Examine these radiographs.
What are your key radiographic findings and how do they influence your surgical planning?
Candidate: The radiographs show severe medial compartment osteoarthritis, classified as Kellgren-Lawrence Grade IV. There is joint space narrowing, subchondral sclerosis, and large osteophytes. The mechanical axis is in varus. For surgical planning, I need to restore neutral alignment by performing a medial release and potentially using a posterior-stabilized implant to compensate for the ligamentous laxity.
Failing to mention the mechanical axis assessment on full-length films or forgetting to address the fixed flexion deformity (FFD). Candidates often jump to "do a TKA" without discussing the specific soft-tissue balancing challenges posed by the medial-sided pathology and the need to achieve a rectangular gap in both flexion and extension.
The radiographs confirm KL Grade IV end-stage tricompartmental OA. Planning must involve: 1. Alignment: Use full-length standing films to assess mechanical axis deviation and determine the degree of varus. 2. Bone Cuts: The distal femoral cut should be planned at 5-6° valgus; the tibial cut should be perpendicular to the mechanical axis with a 5° posterior slope. 3. Gap Balancing: I anticipate a tight medial compartment and a relatively loose lateral compartment. My plan includes a sequential medial release (deep MCL, semimembranosus, and posteromedial capsule) in extension to achieve a symmetric, rectangular extension gap, followed by checking the flexion gap, ensuring the posterior femoral cuts are correctly rotated (3° external) to balance the joint.
During your medial release for this varus knee, how do you decide if you have done enough, and at what point do you risk creating an iatrogenic valgus instability?
Candidate: I perform sequential releases starting with the deep MCL, then the semimembranosus, and finally the superficial MCL if necessary. I check the balance using spacer blocks in both flexion and extension. If the medial side is still tighter than the lateral side, I continue the release. I know I have done enough when the gaps are rectangular and balanced.
Ignoring the danger of releasing the superficial MCL (sMCL). The sMCL is the primary restraint to valgus stress; if it is completely detached from the tibia without repair or if the gap becomes wider medially than laterally, the knee will be unstable in valgus, potentially requiring a constrained implant or hinge.
The goal is a balanced, rectangular gap. I use laminar spreaders or spacer blocks to assess tension. I perform the release in a tiered fashion: 1. Deep MCL and posterior capsule. 2. If still tight, release the semimembranosus. 3. Only as a last resort do I subperiosteally elevate the sMCL from the tibia. I risk valgus instability if I over-release the sMCL or if I perform an excessive tibial resection, which increases the gap size. If the knee becomes unstable in extension, I would consider a more constrained poly or a stem to bridge the gap; however, with meticulous stepwise release, this is rarely necessary in primary TKA.
