chapter 13: Surgical Treatment of Patellofemoral Chondrosis and Arthrosis
PATELLOFEMORAL JOINT RESURFACING IN KNEE JOINT REPLACEMENT SURGERY
Rand (85) has pointed out that extensor mechanism problems are the most common cause of re‑operation after total condylar knee replacement. Problems include instability of the patella, patella fracture, wear debris, soft tissue impingement, rupture of the patellar ligament, loosening of the patellar implant, and infection. He has also pointed out that there is a very high incidence of complication following isolated revision of a total knee patellar component (86). Consequently, precision in resurfacing the patellofemoral joint is extremely important at the time of knee replacement.
Koshino (87) has noted some tendency to develop mild patella baja following knee joint replacement. In 56 kinematic knee replacements, Johnson and Eastwood (88) noted 50% patellofemoral problems postoperatively, with 13 subluxations and 15 patients with anterior knee pain. Postoperative patellar tilt and displacement are common postoperatively (89) following knee replacement. Kirk et al (90) reported his results following realignment of the unstable extensor mechanism after patellar dislocation as a complication of total knee replacement. Using a Trillat procedure in fifteen patients, there were no recurrent dislocations 2 years following revision.
Knee replacement without resurfacing the patella in selected patients with good cartilage yields satisfactory results (91). In many patients, however, patellar resurfacing will be necessary at the time of knee joint replacement. A minimum of 15 mm of patellar thickness should be maintained at the time of patellar resurfacing according to Reuben et al (92). Rand (93) has reported that patellofemoral problems can be markedly reduced by using precise techniques, reducing patellar height 2 mm from the preoperative level, and taking care to balance the patella in the prosthetic trochlea.
Medial placement of the patellar component on the excised patellar surface creates better tracking, and slight external rotation of the femoral component appears to enhance patellar component stability (94). These authors also pointed out that in‑setting of the patellar implant may provide greater stability and better alignment of the patellofemoral joint than on‑laying the prosthesis.
There are some who say that total knee joint replacement is preferable to isolated patellofemoral resurfacing, particularly in elderly patients. When there is generalized or even two‑compartment arthritis, this approach has merit. When disease is restricted to the patellofemoral joint, however, most patients will respond favorably to treatment of the one compartment without resurfacing in most cases. If resurfacing is necessary, the surgeon may consider replacement of the patellofemoral joint alone in carefully selected patients, or total knee replacement in elderly patients.
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