Arthrofibrosis is probably the most common cause of knee stiffness in patients with mechanically sound reconstructions [4, 18]. These patients develop adhesions or dense scar within the joint or extensor mechanism that either act to tether or mechanically impede full joint motion. Fibrous nodules may also form on the undersurface of the quadriceps tendon leading to patellar clunk syndrome, particularly in posterior-stabilized designs. Although this syndrome responds well to arthroscopic resection of the fibrous nodules, it is not commonly associated with diminished range of motion [19]. Attempts to identify predisposing factors for the development of arthrofibrosis have been largely unsuccessful. Thus, preventive measures are limited. A prolonged period of immobilization is certainly a causative factor. Currently, most joint surgeons implement aggressive rehabilitation in the postoperative period in an attempt to decrease the incidence of this complication. At many institutions, this often includes the use of continuous passive motion, the efficacy of which is uncertain. Several studies have concluded that continuous passive motion has no effect on range of motion when measured at 3 months and 1 year [5, 7, 20]. These studies do, however, demonstrate significantly greater flexion in the early postoperative period for patients who were treated with continuous passive motion .

In patients with stiffness following implantation of posterior cruciate retaining devices , several authors have suggested tightness or contracture of the posterior cruciate ligament as the etiology [17, 21, 22]. Significant improvement in range of motion following open or arthroscopic release of the posterior cruciate ligament was achieved in the majority of these patients.

The etiology of stiffness following knee arthroplasty is often technique related, which often can be elucidated on radiography or by physical examination. These patients can be distinguished from patients with arthrofibrosis by comparing their postoperative motion with that achieved at surgery. Limitation of motion, if technique related, will be present at the time of surgery. Prior to attributing these imperfections to surgical error, one must consider a few points. While it should be the goal of every surgeon to implant prosthetic components in anatomic position and perfect alignment to allow full range of motion, this is not achievable in all cases due to variations in anatomy and technical limitations available. Because there are limits to the sizes and configurations of implants used and the variations in anatomy are infinite, compromises are often necessary after considering the alternatives.

Five broad categories of technical imperfections can lead to knee stiffness. These are retained bone or osteophytes of the posterior femoral condyles, malalignment, imbalance of the extension gap and flexion gap, improperly sized components, and improper reconstruction of the patellofemoral joint.

At the time of primary knee arthroplasty, bone or osteophytes along the posterior femoral condyles and femur should be removed, if possible. This is best accomplished in the following fashion: With a trial femoral component in position, a curved osteotome is used to resect any excess posterior bone. The trial component is used as a template so the surgeon can precisely remove the correct amount of bone and often includes the removal of a small portion of normal posterior femoral condyle. If resection of posterior bone is incomplete, the remaining bone can impinge on the posterior edge of the tibial component or tibia, resulting in a mechanical impediment to full flexion. Residual posterior bone can be identified on a lateral radiograph and should be looked for when a patient presents with a stiff knee (Fig. 24.2).

Restoration of proper mechanical alignment is critical to ensure both proper function and longevity of a knee implant [23]. This includes alignment in sagittal, coronal, and rotational planes. Significant malalignment in any of these planes can result in decreased range of motion. Standing 3 foot anteroposterior and lateral radiographs are most helpful in assessing alignment and should be obtained for any patient in whom revision surgery is being considered. In the coronal plane, it is not uncommon to see errors of up to 3° on either the femoral or tibial component [1]. It would be highly unusual for this amount of malalignment to result in motion limitation [1, 23]. However, when measurements exceed 5°, the likelihood of resultant loss of motion increases dramatically. In the sagittal plane, excessive flexion or extension of the femoral component can lead to limitation of motion, but the degree of error must be quite large and is rarely seen as the cause. This is not the case with the tibial component, in which a relatively small degree of malalignment in this plane can significantly affect motion. The slope of the tibial prosthesis relative to the long axis of the tibia should be carefully evaluated. Excessive posterior slope may result in lack of full extension and instability in flexion. Anterior slope (i.e., hyperextension of the tibial component) is likely to lead to recurvatum deformity and lack of full flexion. Of course, the amount of posterior slope designed into the particular component implanted must be taken into account when evaluating the radiograph. When possible, comparison of the patient’s preoperative anatomic tibial slope to that achieved postoperatively can be enlightening.

Improper balance of the extension and flexion gaps can clearly lead to stiffness following knee arthroplasty. This includes both asymmetry of the individual gap and mismatch between gaps. If the extension gap is tight relative to an appropriate flexion gap, lack of full extension is the result. Conversely, if the flexion gap is tight relative to an appropriate extension gap, limited flexion is observed.

Incorrect sizing of the implant affects knee motion. For both the femoral and tibial components, appropriate anteroposterior dimension is most important for restoration of knee mechanics. Oversizing of the femoral component results in tightening of the collateral ligaments in flexion. The resultant flexion/extension gap mismatch leads to incomplete flexion. Undersizing of the tibial tray, when combined with excessive anterior placement on the tibia, also affects motion. In this situation, the uncovered posterior cortex of the tibia leads to a mechanical block from contact between the posterior femur and tibia as the knee is flexed. Finally, oversizing of the composite thickness of the tibial component and liner results in a knee that is globally too tight, limiting both flexion and extension.

Complications associated with reconstruction of the patellofemoral joint can result in decreased flexion [18, 24]. Maltracking or tilting of the patella can have an effect on motion by both mechanical and pain-mediated pathways. Patients with these findings often demonstrate an unwillingness to fully flex their knees. If the reconstructed patella is too thick, increased forces across the patellofemoral joint may impede flexion.

Excessive internal of the femoral and tibial components has also been associated with postoperative stiffness, either individually or summed [25]. Internal rotation of either component may contribute to patellar maltracking giving patients the sense that the patella is going to subluxate or dislocate with deep flexion. Patients will avoid deeper flexion to prevent this sensation. In addition, internal rotation of the components contributes to alterations in the flexion gap. Whereas, internal rotation of the femur may cause an excessively tight medial flexion gap, tibial internal rotation can limit the amount of femoral rollback possible. Both mechanisms may limit flexion.

Elevation of the joint line, which can occur with over-resection of the distal femur, under-resection of the tibia or excessive soft tissue release, can also contribute to loss of flexion [26, 27]. This condition, often termed “pseudo-patellar baja,” can also contribute to extensor lag, impingement of the patella against the tibial polyethylene or tibial plate, anterior knee pain, increased energy expenditure, and rupture of the patellar or quadriceps tendons [28].

Identification of technical imperfections when presented with the stiff knee is relatively straightforward. The difficulty lies in whether those findings are the actual cause of stiffness. The surgeon must remember that technical imperfections can be identified in many well-functioning total knee replacements.

Delayed hypersensitivity reactions after total knee arthroplasty are rare and poorly understood. However, these patients may present with knees that are painful and stiff. Current literature on metal hypersensitivity causing stiffness is limited to small case series and case reports so the incidence is unclear. In these reports, patients underwent extensive preoperative workups, which ruled out infection. Intraoperative histopathology revealed a thickened synovium and adhesions with either a predominantly lymphocytic or histiocytic monocellular response, consistent with a type IV allergic reaction. Symptoms resolved in each of these reports after revision to ceramic or zirconium femoral components and titanium tibial components [29–31].

Anecdotal cases of loose bodies within the joint have been described. In one case report, an intra-articular fragment of methyl methacrylate was identified [32]. Knee motion was restored after arthrotomy and removal of the offending loose body. Fracture of the polyethylene should also be considered when determining the cause of knee stiffness.