Prevention is the best way to treat a stiff knee. However, correct diagnosis is the first step to start a correct treatment. Beyond the special cases such as arthrofibrosis, heterothopic ossifications, and reflex sympathetic dystrophy whose treatment has been previously discussed, general treatment consists of the following options: manipulation, artrolysis (open or arthroscopic), and revision surgery.
Closed manipulation
This is a debated option, and its timing is critical. This procedure seems to accelerate ROM recovery in patients with slow and difficult rehabilitation rather than allowing for a greater final ROM. Some authors suggest a closed manipulation in all patients not reaching 90° of flexion on the 10th day after surgery [
27], others wait for at least 2 weeks [
28]. The incidence of closed manipulations is therefore 54 and 23%, respectively. Esler et al. [
29] suggest a closed manipulation in all patients not reaching 80° of flexion regardless of the delay from the surgical procedure. In general, the commonly accepted indication is a postoperative flexion inferior to 90° at 6 weeks, and the earlier this manipulation is performed, the more satisfactory is the result as showed by Daluga [
30]. In the case of a too early manipulation, a risk of skin and soft-tissue damage is present; thus, a delay of at least 3 weeks from the surgical procedure is indicated. Its aim is to strip the fibrous bands that originate in the suprapatellar pouch in the case of incorrect rehabilitation. These bands become stronger and stiffer beyond 6 weeks with increased risk of complications such as patellar or femoral fracture or extensor mechanism rupture in the case of closed manipulation.
Manipulation should be performed under general or regional anaesthesia to provide adequate muscle relaxation, reducing the risk of complications. Once the effective ROM is recorded, a gentle force is applied to force the maximum flexion; mobilization of the patella is indicated, as it destroys the adherences in the suprapatellar pouch. This maneuver should be repeated several times for a complete lysis of fibrous bands. Postoperative management consists of continuous passive motion set to the maximum flexion and extension obtained. Pain control is essential: an epidural catheter is set in place for 24–48 h. Some authors stress the importance of pain management during rehabilitation and report that proper pain control reduces the necessity of closed manipulation from 9 to 1% [
31].
Results seem satisfactory in the case of correct indications and precise technique: Yercan reports a ROM improvement from 67 to 117° [
32], Pariente et al. [
33] from 71 to 102° with his modified technique, while Scranton [
5] reports an average gain of 36 and 35° if the manipulation is performed within 12 weeks and beyond this limit, respectively.
Arthroscopic arthrolysis
Arthroscopic arthrolysis consists of lysis of direct adherences and is indicated in the case of arthrofibrosis in patients with a difficult rehabilitation. The ideal indication is a painless, stiff knee that has not improved after 3–6 months of conservative treatment, as reported by Court [
34]. On the other hand, poor results are reported in painful stiff knee; this seems to be a consequence of wrong diagnosis [
35].
This procedure guarantees a wide access to the suprapatellar pouch thus allowing good flexion recovery, while the access to the posterior part of the joint is extremely difficult or impossible. Thus, it is less effective in the case of extension lag. A PCL release or sacrifice is possible and is indicated in cruciate-retaining implants when a tight PCL is found. Its section leads to an immediate flexion gap increase and confirms that the diagnosis was correct. Foreign body removal (cement) is also possible under arthroscopy. Classic portals are sufficient in the majority of cases; if patellofemoral fibrosis is expected, then additional superior portals (medial and lateral) may be indicated. Synovial and scar samples are taken for a microbiological and histological analysis.
Jerosch describes a standard technique that consists of release of all fibrous bands in the suprapatellar pouch, re-establishing of the medial and lateral gutters, patellar release, and removal of remaining meniscal tissue or anterior cyclops. He reports a mean postoperative flexion of 119° and a decrease in extension lag from 27 to 4° [
36].
Results after arthroscopic arthrolysis are rather controversial in the literature. Bocell et al. [
35] report an increase in postoperative ROM in 43% of the patients, Williams et al. [
37] an average increase in ROM of 30.6°, while Mont et al. [
38] report an average improvement of 31° in 94% of the patients. Best results are obtained in the case of isolated patellofemoral fibrosis. As for the closed manipulation, best results are obtained in the case of early procedure. Most authors recommend not delaying beyond 6 months to avoid the scar tissue becoming strong and resistant. The importance of an aggressive postoperative protocol consisting of continuous passive motion and proper pain control after arthroscopic arthrolysis is now widely accepted [
39]. In the case of severe ROM limitation, arthroscopic treatment alone is less effective, as demonstrated by Scranton [
5], who noted worse results in the case of ROM ≤ 60°.
Open arthrolysis
Keeney et al. [
40] recommend open arthrolysis in the case of a severe ROM limitation after TKA with no component malposition and after a proper conservative treatment performed for 6 months after surgery. It may be associated with polyethylene insert or patellar component exchange. Complete exposition may be difficult due to adherences, and posteromedial corner release facilitates this maneuver. If patellar eversion is impossible, then tibial tubercle osteotomy or quadriceps tendon snip or VY plasty may be indicated. Suprapatellar pouch and medial and lateral gutters should be explored to look for fibrous bands. Posterior release is indicated to improve extension, while a 1- to 2-cm proximal transfer of the tibial tuberosity increases knee flexion and raises the patella with a minimal loss of quadriceps strength. Scuderi [
8] proposes the quadriceps snip and tendon lengthening to improve maximum flexion with no extension or strength loss. Patellar resection is indicated in the case of overstuffing. In the case of flexion contracture, polyethylene downsizing is indicated.
Unfortunately, only a few reports are available in the literature concerning the results of open arthrolysis in the treatment of a stiff knee. In a Sofcot series, flexion and extension gains were 20 and 18°, respectively [
41]; Hutchinson reported an increase from 55 to 91° 6 months after open arthrolysis [
42]; and Pretzsch showed an increase in knee flexion from 46 to 90° and a decrease in flexion contracture from 11 to 7° [
43]. In contrast, Babis reports poor results in the case of open arthrolysis and polyethylene exchange for stiff knees with fixed and well-aligned prosthetic component [
44].
Revision surgery
In the case of documented surgical errors, any attempt to improve ROM must consider the resolution of these errors, making revision surgery necessary. Accurate analysis of these errors is essential to plan the revision correctly and to evaluate the expected benefits. In fact, functional results are usually unpredictable and ROM recovery may be poor. The incision should consider the skin contracture and fibrosis; scar excision should be avoided; and in the case of multiple incisions, the most lateral should be preferred. As previously mentioned, patellar tendon avulsion may occur due to its shortening, and fibrosis, tibial tuberosity osteotomy, quadriceps snip, or VY plasty are often required. Scar-tissue removal is performed in the same manner as in the case of open arthrolysis. Component stability, evidence of polyethylene wear, and patello-femoral track are carefully examined. Component removal may lead to bone stock loss especially in the case of uncemented implants, requiring wedge and augmentations to address this loss.
Great care should be taken with the patella, which is a cause of stiffness requiring revision surgery in 55% of the cases as shown by Bonnin et al. [
45]. Patellar thickness is measured, since it is a common cause of stiffness when it is excessive. In the case of thickness greater than 26 mm in males and 24 mm in females, a resection is indicated [
46]. Soft-tissue balance is performed both in flexion and extension, and minimal symmetrical laxity in extension should be preferred to stiff knee. Considering the frequent recurrence of stiffness, some authors prefer to obtain a hyperextension of 5° at the end of revision surgery [
47]. It has been proved that a tibial overresection of 1 mm increases the extension space by 4° [
48].
The problem of joint-line level is still debated. Epicondiles are a good anatomical reference in joint-line restoration as described by Griffin. In unaffected knees, the medial epicondile is 27.4 ± 2.9 and 29.7 ± 2.7 mm from the joint line in coronal and axial planes, respectively. Lateral epicondile is 24.3 ± 2.6 and 25.0 ± 2.6 mm from the joint line in coronal and axial planes, respectively [
49]. Excessive joint-line elevation leads to a patella baja and to loose collateral ligaments in flexion. Figgie et al. [
19] state that an elevation up to 8 mm has no major consequences for the postoperative result. Unfortunately, in revision surgery, the epicondiles are not always clearly detectable; thus, the evaluation of the joint-line height may be difficult. Therefore, the distance from the inferior pole of the patella to the joint line has been proposed as a measure, and values greater than 1 cm are necessary to restore a proper height [
19]. Component malpositioning in the frontal, sagittal, and coronal plane should be corrected to avoid stiffness recurrence. Frontal malalignments and rotational tibial and femoral errors should be corrected, as they affect both patellofemoral kinematics and soft-tissue balance. Postoperative results are unpredictable both in terms of articular recovery and clinical improvement.
Haidukewych et al. [
50] in a series of revisions for stiffness report a ROM improvement from 40 to 73°, 66% of satisfactory results, and a further revision rate for stiffness of 25%. Dorr and Nicholls report fair and unpredictable results in the case of revision. Positive prognostic factors were malpositions and previous osteoarthrosis, and negative factors were patella baja and previous rheumatoid arthritis [
4]. Nelson et al. [
10] report an improvement of flexion contracture from 11.3 to 3.2° and flexion improvement from 65.8 to 85.4°. A postoperative ROM improvement was present in 93% of the patients.
Keeney compared the results of a limited approach (soft-tissue release and tibial insert downsizing) with those of a complete revision surgery. In the first group, there was an improvement in postoperative ROM (25.7°), clinical score (37.8 points), and functional score (20.8 points). In the second group, the improvement in postoperative ROM was 17.9°, in functional score was 3.6 points, while there was a decrease of 1.0 point in clinical score [
40].
Bonnin [
45] reported a ROM increase of 41° with associated symptoms improvement. In a SOFCOT series, there was a flexion improvement of 35° with an average postoperative flexion of 83°; moreover, an improvement in flexion contracture and pain score was noted [
41].