Flexion Contracture Associated With Total Knee Arthroplasty

A fixed flexion contracture can result from several disease processes, including osteoarthritis, rheumatoid arthritis, and posttraumatic arthritis. Often a common pathway starts with pain and leads to decreased motion and posterior capsular scarring. The scarring promoted by the inflammatory component of rheumatoid arthritis also plays a role. In arthrosis resulting from osteoarthritis or trauma, osteophytes play a significant role. Osteophytes develop posteriorly and in the intercondylar area ( Fig. 7.1 ). The intercondylar osteophytes form a mechanical block to extension, and they alter cruciate kinematics. Osteophytes often overgrow the entire intercondylar notch in advanced osteoarthritis, obscuring the posterior cruciate ligament origin and causing attritional rupture of the anterior cruciate ligament.

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Posterior osteophytes and intercondylar osteophytes ( arrows ) play a major role in flexion contractures associated with osteoarthritis.

Posterior osteophytes can impede flexion because of impingement and scarring. They limit extension by scarring and tenting up the posterior capsule. When a flexion contracture becomes long-standing, secondary hamstring contracture can occur.

The goals of total knee arthroplasty (TKA) are to provide adequate pain relief along with a knee that is stable and has a functional range of motion. The amount of knee flexion necessary for various activities of daily living is discussed in Chapter 6 . The amount of knee extension necessary for a good functional result remains controversial. In a gait analysis study, Perry and colleagues reported in 1975 that −15 degrees of extension was necessary for a good functional result. In my experience, a permanent flexion contracture of 15 degrees after TKA may or may not be dysfunctional for the patient. On the other hand, I have yet to see a patient with a 10-degree flexion contracture report disability. In other words, −10 degrees of extension is acceptable, −10 to −15 degrees is borderline, and −15 degrees or more is not acceptable.

Another controversy exists about how much of a preoperative flexion contracture has to be corrected at the time of surgery. The 1989 article by Tanzer and Miller is often quoted. They reported a small series of 35 TKAs with preoperative flexion contractures of less than 30 degrees. Only five of the knees in the series had flexion contractures greater than 20 degrees. The authors noted that the flexion contractures tended to improve after surgery and complete correction intraoperatively was not necessary. To an extent, I am in agreement with this, as discussed later. I think it is very important not to overcorrect for flexion contractures, resulting in a knee with hyperextension. In short, I would rather have a knee with a 5-degree contracture than one with 5 degrees of hyperextension. Similarly, I would rather have a knee with 10 degrees or 15 degrees of a flexion contracture rather than 10 degrees or 15 degrees of hyperextension.

Treatment Options

Treatment options for flexion contractures can be sorted into three categories: preoperative, intraoperative, and postoperative measures. Postoperative measures are discussed in the later section, Ancillary Measures.

Preoperative Measures

Preoperative measures such as manipulation and serial casting or dynamic splinting are usually amenable only in patients with inflammatory arthritis without osteophyte formation (which can cause a bony block to extension). This type of treatment is especially appropriate for the adult patient or the patient with juvenile rheumatoid arthritis with bilateral hip and knee flexion contractures about to undergo both hip and knee replacement surgery. In this situation, the hip arthroplasty is almost always performed first (see Chapter 9 ). Although the patient is under anesthesia for the hip surgery, the knee is gently manipulated (stretched) for 3 to 5 minutes. Maximal extension is recorded, and a long-leg cast is applied at approximately 5 degrees less than the maximal extension. The cast must be well padded to avoid undue skin pressure. The following day, the cast is bivalved and lined as a resting cast. Ideally, the anesthetic used is an epidural, which can be left in place for several days, permitting daily manipulations with a new cast until progress ceases. In patients with rheumatoid arthritis, I have seen preoperative flexion contractures of 90 degrees almost entirely corrected before attempting TKA ( Fig. 7.2 ). Obviously, this method is preferable to excessive bone resection to achieve an adequate extension gap. Because these patients are always osteopenic, care must be taken to avoid forceful manipulation and the possibility of a fracture (usually supracondylar). As noted previously, this preoperative manipulation method is not appropriate for the osteoarthritic patient with a bony block to extension.

Intraoperative Measures

Various intraoperative measures can be used to correct a flexion contracture. It may be difficult to expose this knee, and the measures I recommend are covered in Chapter 6 . The treatment options include removal of osteophytes both anteriorly and posteriorly. The posterior capsule can be stripped from both femur and tibia. Additional distal femoral resection is necessary for severe contractures. Occasionally, extra proximal tibial resection will be appropriate in the presence of patella baja. The amount of posterior tibial slope applied to the tibial resection should be zero rather than the usual 3 to 5 degrees. Finally, PCL substitution is helpful to facilitate release of posterior structures and correct posterior tibial subluxation, which either preexists in severe contractures or occurs as extension is achieved ( Fig. 7.3 ).

Osteophyte Removal

Anterior osteophytes in the intercondylar notch can build up and limit extension because of impingement. They will be removed with routine bone resection, allowing room for adequate extension to occur. Posterior osteophytes are more common in varus knees than valgus knees and more prevalent medially than laterally. The posterior capsule often contracts around the osteophytes, and their removal releases the posterior capsule enough, in many cases, to gain full extension with routine amounts of distal femoral bone resection when preoperative contractures are 15 degrees or less. The posterior osteophytes are best accessed and cleared after preliminary femoral and tibial preparation.

The trial femoral component is inserted without a trial tibial component. The knee is flexed and held upward with a bone hook. A curved ⅜-inch osteotome is passed sequentially tangent to the metallic posterior condyles so that it removes any uncapped femoral bone and frees up the posterior osteophytes. The same maneuver is an efficient way to strip some of the posterior capsule from its femoral attachment. After the contour of the femoral component has been outlined on the posterior condylar bone, the trial femur is removed and the uncapped femur and remaining osteophytes are resected ( Fig. 7.4 ). An osteotome can also be used to strip the posterior capsule from the back of the tibia. I rarely did this maneuver, however, and gained most of the capsular stripping from the femoral side.

Additional Distal Femoral Resection

The initial amount of distal femoral resection should be based on the thickness of the femoral component to be implanted. If the component is 9 mm thick, for example, an anatomic resection would consist of 9 mm including cartilage. If the amount resected is based on bone, a conservative initial distal femoral resection should be 7 mm, allowing for 2 mm of cartilage. It is important not to perform too much initial distal femoral resection in a PCL-retaining knee. This could lead to a flexion–extension gap mismatch that is difficult to repair. For example, too much distal femoral resection will lead to a knee that is tighter in flexion than in extension. To correct this, the surgeon will have to perform a PCL release, apply more posterior slope to the tibial resection, or consider downsizing the femoral component to increase the posterior condylar resection and increase the flexion gap without affecting the extension gap. A final solution would be to cement the femoral component proud of the distal cuts. These four solutions can be effective but will not need to be considered if the surgeon prepares the knee initially so that, if anything, the extension gap is tighter than the flexion gap. The solution to this mismatch is simple: the surgeon revisits the distal femoral cut to increase the extension gap without affecting the flexion gap. The chamfer cuts must also be redone, but the entire maneuver will take only a few minutes. For this reason, I used the method of increasing the distal femoral resection for flexion contracture only in knees with initial flexion contractures greater than 15 degrees when the patient is under anesthesia. I increased the distal femoral resection by 2 mm for every extra 15 degrees of flexion contracture. For example, if a knee has 0 to 15 degrees of flexion contracture, the distal resection for a 9 mm femoral component is 7 mm of bone. For a flexion contracture between 15 and 30 degrees, the distal resection is 9 mm of bone. Between 30 and 45 degrees of flexion contracture, the distal resection is 11, and over 45 degrees it may go as high as 13 mm. I would never increase the distal resection more than this amount because the level of the origin of the collateral ligaments is soon approached and the resultant elevation of the joint line significantly disturbs the kinematics of the knee. This elevation of the joint line will usually require PCL substitution and even Total Condylar III constraint if significant joint line elevation leads to flexion instability.

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