The patient had undergone spinal surgery due to lumbar canal stenosis with posterior instrumentation when she was 55 years old; the spinal implants were removed 3 years post-operative.
At the time of presentation, she was unable to walk even with a walker. Deformity, swelling, and effusion were noted in both knees. The right knee was extremely valgus and the left was contrarily varus. There was no evidence of redness or heat. The range of motion of the right knee was 15-90(recurvatum deformity), while that of the left knee was 5-100. Bilateral global laxity was noted with greater severity on the right side. Lateral patellar subluxation was observed in the right knee. The manual muscle testing (MMT) grades of the bilateral lower limbs indicated good strength (4/5). The bilateral patellar tendon reflex and Achilles reflex were depressed. There was a severe sensory loss of touch, pain, temperature, and vibration in the bilateral lower limbs, especially in the distal region.
A blood test showed normal inflammatory parameters (white blood cell count, 4.9 x 109/L; neutrophils, 2.7 x 109/L; and C-reactive protein, 0.12 mg/dL). Her glycated hemoglobin level was normal (5.5%). Treponema pallidum hemagglutination, T-SPOT.TB, and antinuclear antibody tests were all negative.
A plain radiograph of the right knee showed severe valgus and recurvatum deformity with a severe bone defect at the posterolateral tibial plateau (Fig. 1), while that of the left knee showed varus deformity with a large calcified loose body in the suprapatellar pouch (Fig. 2). Moreover, lateral patellar subluxation of the right knee was evident (Fig. 3). The anatomic femorotibial angle was 140at the right and 180at the left (the so-called windswept deformity) (Fig. 4). All other joints were normal.
After admission, bed rest and arthrocentesis relieved her knee pain. A culture of the synovial fluid was negative. An examination of the nerve conduction velocities in her legs showed us that she had severe sensory neuropathy of the bilateral lower limbs. Based on her medical history, we believed that this patient had developed bilateral neuropathic arthropathies caused by lumbar spinal canal stenosis. Because she could not walk due to instability, we decided to perform a staged bilateral TKA.
We performed TKA of the right knee first because its deformity was more severe. We chose a rotating hinge prosthesis (Modular Rotating Hinge; Stryker, Mahwah, NJ, USA) and performed the procedure using a medial parapatellar approach. Modular stems were used both on the tibial and femoral implants. The procedure included autologous bone grafting and metal augmentation for tibial bone loss and patella replacement and lateral retinaculum release for patella subluxation.
She demonstrated right drop foot immediately after the first operation. We prescribed an ankle-foot orthosis for her right ankle and started her rehabilitation therapy. The muscle power of her tibialis anterior slowly improved (MMT 3) over 3 months postoperatively. The active range of motion of the right knee was 5-95. However, the patient was unable to walk because of the left knee instability.
We decided to then perform TKA for the left knee. We selected a constrained condylar prosthesis (Triathlon TS; Stryker, Mahwah, NJ, USA) using the same approach as in the first surgery. Intraoperatively, we removed a large loose body that was found in the suprapatellar pouch and performed a lateral retinaculum release and patella replacement. The active range of motion of the left knee was 0-95and the patellar tracking was good.
At the time of the 6-month follow-up, both knees were stable and in good alignment. There were no signs of loosening or fracture (Fig. 5). The patient experienced no pain and was able to ambulate throughout her house with a walker.