We can either use a custom femorotibial spreader or a femoral suspension device introduced in the intramedullary canal to elevate the femur at 90° of knee flexion, allowing a good view of the posterior segment of the joint, taking care to avoid damage to the popliteal vessels and nerves. A curved osteotome and bone nibbler can be used sequentially, medially, and laterally, changing the position of the laminar spreader for osteophyte removal and elevation of the capsule from the posterior femur.

For severe flexion contractures, greater than 40°, this approach can be used to elevate the tendinous origins of the gastrocnemius muscles medially and laterally [12, 13].

Techniques of transverse sectioning of the posterior capsule, initially described by Insall, should not routinely be used. Zaidi [26] described that with knee flexion, the neurovascular bundle is displaced anteriorly and can lie tethered against the posterior capsule, representing a major risk of damage.

We prefer to do tibial resection after distal femoral cut is complete. The goal of tibial resection is also to reestablish the tibial joint line, planned to be perpendicular to the tibial shaft axis in the coronal plane. The amount of resection required depends on the degree of the deformity and ligamentous tension.

The amount of posterior slope depends also on the deformity and the type of implant used. When using a posterior cruciate-retaining TKA, the slope should be set at 5–10°, whereas in cruciate-substituting designs, the slope should be set to neutral because the PCL cut increases the flexion gap by 2 mm more than the extension gap (9).

The flexion contracture deformity presents a flexion gap that is generally greater than the extension gap, and therefore, a resection without posterior slope will facilitate the flexion/extension gap balancing [13].

After bone resections and osteophyte removal are completed, the next step will be balance of the flexion/extension gaps and of the medial and lateral collateral ligaments with either spacer blocks or trial components [3, 13, 21, 25]. A step-by-step adjustment of the soft tissue releases and further removal of osteophytes should be perfomed (Fig. 11.3).

If flexion contracture deformity remains after all releases are done, then further distal femoral resection must be done to balance the flexion/extension gap and obtain full extension [2, 13, 17]. Additional 2 mm of bone resection in posterior cruciate-retaining design, but in the presence of severe flexion contracture deformity the joint line elevation can be rarely extended by 4 or 6 mm [14]. This purpose can be better accomplished with posterior cruciate-sacrificing design [14], because in these severe cases the PCL is contracted and difficult to balance (Fig. 11.4).

With severe flexion contracture, where greater amounts of distal femoral resection are required to obtain full extension, all structures anterior to the posterior capsule are lax in full extension. A posterior stabilized constrained device may be required for varus/valgus stabilization during all the arc of motion.

A common error is to begin by resecting too much distal femur resulting in an elevation of the joint line and midflexion instability. Our attention must first be directed to soft tissue balancing, posterior capsule release, and osteophyte removal [2, 3, 11, 13].

Our philosophy is to use an implant system offering a continuum of constraint or at least to have on the operating theater options for specific indications presented by the patients after major ligament releases or bone resection. It is advisable to have a hinged implant ready when undertaking such surgery.

A surgical algorithm was proposed by Bellemans and associates consisting of four steps: (1) mediolateral ligament balancing with resection of all osteophytes and overcorrection of 2mm of the distal femur, (2) progressive posterior capsule release and gastrocnemius release, (3) additional resection of up to a maximum of 4 mm of the distal femur, and (4) hamstrings tenotomy. With flexion contractures greater than 35°, additional resection of the distal femur and hamstrings tenotomy were performed in only 28.6 % and 22.9 % of cases, respectively.

The surgical concept seems to be that over-resection of the distal femur by more than 2 mm should be avoided until all osteophytes have been removed and the knee is correctly balanced medially and laterally. Complete correction of the deformity, with no help from the surgeon, must be obtained intraoperatively at the end of the procedure [3, 11, 13].

Preoperative flexion contracture severity does not correlate with the residual contracture. That is to say, a mild flexion contracture is not easier to correct than a severe one [14]. Long ago Firestone et al. [4] showed that the degree of perioperative residual flexion contracture impacts final extension recovery.

In patients with flexion contractures greater than 45/60° [11], reaching full extension is not possible without marked shortening of the femur. In these rare patients nowadays in developed countries, a preoperative traction can often decrease the contracture below 30/45° [12]. The options are to perform a femoral shortening and accept an extensor lag or allow a residual 10–15° of flexion contracture [13] often reasonably well tolerated by the patients. This minimized the risk of stretch injuries of neurovascular structures.

With bilateral severe flexion contracture, as in deformities over 10°, the TKA must be done simultaneously [11]. If not, the operated knee becomes longer than the contralateral side, and to compensate for the leg discrepancy, the patient will walk with the operated knee flexed. Over a period of several months, even with the proper rehabilitation program, this leads to a flexion contracture.

When patient’s medical problems do not allow for a simultaneous TKA, then the optional treatment is to place a heel lift on the shoe of the nonoperated leg until the time for its surgery.

The presence of severe flexion contracture deformity may require at the end of the procedure a proximal realignment of the extensor mechanism to strengthen it, giving the quadriceps muscle some mechanical advantage and minimizing the risk of extensor lag. This can be done by lateral and distal advancement of the vastus medialis obliquus [13].