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The extensor mechanism of the knee consists of the quadriceps muscles and tendon, the patella, patellar tendon and supporting medial and lateral retinaculum. Rupture of the patellar ligament is one of the most serious complications after total knee arthroplasty. The etiology is multifactorial. Given the complexity of these cases, which often include multiple medical problems, connective tissue abnormalities, or multiple previous operations on the same knee, its comorbidity. Although patellar tendon disruption during TKA is a rare occurrence, all surgeons performing this procedure should be ready to handle this potentially disastrous complication.
Early accurate diagnosis is important, as the method of treatment and the outcome depend on this. However, other factors include the time since injury is very important as those treated acutely have a more favorable outcome.
Rupture of the patellar tendon is most commonly caused by a violent contraction of the quadriceps muscle against the fixed load of the patient’s body weight with the knee in a flexed position, and occurred as a result from repetitive microtrauma to the fibers of the patellar tendon. The hallmark of a patellar tendon rupture on physical examination is the patient’s inability to actively extend the knee against gravity. This finding, along with a painful, palpable defect in the substance of the tendon and demonstration of patella alta on a lateral radiograph, makes the diagnosis of this condition relatively straightforward.
Complex revision total knee arthroplasty has always required a more generous surgical exposure to prevent rupture of patellar tendon; the most common techniques for extensile exposure are quadriceps snip, tibial tubercle osteotomy, and quadriceps turndown.
It is not surprising that treatment of patellar tendon rupture has not provided good results. For example, primary repair of the tendon alone rarely restores extensor function. Immediate surgical repair of the ruptured patellar tendon is recommended for optimal return of function. A Bunnell-type repair with the use of heavy nonabsorbable sutures through transosseous tunnels with a reinforcing cerclage suture is recommended for a secure repair. In addition, the use of a flexible cable creates a more synergistic construct with the patellar tendon.
The modified technique of using semitendinosus and gracilis tendons (STG) with preserved distal insertions in combined with tension-reducing wire, in treatment of the rupture has several advantages. First, semitendinosus and gracilis tendons are rich in tendon fibers, which are stronger than those of the fascia lata, or quadriceps-patellar retinaculum. Second, by preserving distal insertion of the tendon you provide additional stability during the early stages of tendon bone healing, and retain blood supply to promote healing of the tendon. Third, when the tendons are passed in opposite directions through the tunnels, force is distributed on both sides of original patellar tendon.
In rare instances, allograft tendons are required to span the defect when local tissue is unavailable. It has proven to be successful in most patients. The studies emphasize the importance of tightly tensioning the allograft with the knee in full extension, Failure to provide maximal tension on the graft will result in subsequent extensor lag.
Artificial ligaments can be a useful tool in ligament reconstruction, avoiding the necessity of tendon harvesting procedures and the possibility of donor site morbidity. The use of the LARS ligament is well established in cases of cruciate and collateral knee ligament reconstruction and can also be used for the reconstruction of a neglected patella tendon in an elderly, and low demand patients.
There is no golden standard protocol in rehabilitation program, the extensive rehabilitation program, which is supervised by a physical therapist throughout the process, is a significant factor for a good functional outcome, emphasizing controlled range of motion exercises and quadriceps strengthening, will enhance the results of surgery.
Outcomes after repair have been found to be most closely related to the length of time between injury and repair. Patients who undergo an immediate repair usually achieve a full return of knee motion and quadriceps strength. Patients who undergo a delayed repair have been noted to have limitation of knee flexion, quadriceps weakness, and persistent quadriceps atrophy.