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1. GENERAL ASPECTS
If after injury ligaments remain lengthened or unable to regain continuity, which is commonly the case in cruciate tears, patients may experience an increasing degree of instability. Classically, this occurs when during weight bearing the knee is flexed and rotated. Under these circumstances the leg may give way or buckle, especially if the patient attempts to pivot on the leg or change direction during ambulation. This can be quite disconcerting and even may endanger the patient's life if it happens on crossing a road or working at heights.
Chronic ligament laxity usually involves a number of structures, some of which will have stretched over time. It is henceforth a difficult problem to treat by any simple surgical means. Thereupon it is difficult to improve upon the loss of proprioception (see above) other than ensuring that quadriceps and hamstring muscle groups are well developed and by training the patient to perceive the behaviour of the joint when sudden stresses are applied.
Chronic instabilities will worsen in the presence of a meniscal tear. Although initially menisci may be intact they are exposed to abnormal stresses because of the laxity of the knee. Thus a knee affected by antero-lateral instability and persistent forward subluxation of the lateral tibial plateau is likely to sustain a rupture of the posterior horn of the lateral meniscus. Once torn it further increases joint instability and buckling of the knee might occur.
2. PHYSIOTHERAPY
Before considering any surgical endeavour, the patient should be encouraged to undertake an extensive course of physiotherapy. This will increase quadriceps and hamstring power, the two muscle groups which are essential in providing active knee control. In some cases this might be enough to maintain adequate knee stability during daily activities or low-key sporting activities such as golf. It will also allow the surgeon to judge upon the patient's motivation and physical fitness, both pre-requisites for successful surgical outcome.
3. BRACES
If adequate muscle strength has be obtained and the patient still suffers from symptoms of instability the use of a stabilising knee brace should be considered. Derotation braces can in certain circumstances be sufficient to control lower levels of instability during sporting activities which involve a degree of twisting and turning (tennis, squash etc.). A brace should however be worn judiciously and the patient is best advised to discuss its use with their physician or physiotherapist. As a rule braces should be worn during sporting activities and discarded when strengthening activities are undertaken (gym). There are various types of braces available commercially. It is therefore important to define the type of instability before deciding which brace to recommend. Braces should be measured to the patient's leg size in order to provide a close fit to the knee and leg contours. Varus and valgus laxity can be controlled relatively easily, whilst it is very difficult to prevent rotatory instability, which is often the main feature in chronic laxities. The force achieved to control rotation depends on the lever arms of the brace, hence proximal and distal extensions should reach approximately to the mid-point of thigh and calf respectively. Too long a lever arm might increase stability but will restrict the patient unduly. Modern braces try to provide an acceptable compromise between comfort and ease of application and effective control of laxity (see REHABILITATION & PHYSIOTHERAPY).
4. SURGICAL OPTIONS
It is generally accepted that the indications for surgery in patients presenting with chronic knee instability are often difficult to define with adequate precision. Patients should be motivated and willing to accept a lengthy recovery process. The surgeon should provide the patient with a realistic appraisal of certain limitations and achievable long-term goals. Thereupon patients may be advised not to pursue some forms of sport, particularly those which exposes the knee to a high degree of pivoting and shearing forces.
Patient will have to meet certain criteria in order to be suitable for surgery. In the past it was generally accepted to exclude patients over the age of 45 and those with established signs of joint degeneration. However, these criteria have been relaxed in recent years and it is now common to consider the patients biological age, fitness and sporting ambitions rather than the chronological age as a guide. Most surgeons would still exercise caution regarding late reconstruction when patients present with established degenerative changes. This applies in particular for the presence of eburnised areas where the surface cartilage has been completely eroded (Outerbridge grade IV changes).
Prior to surgery the leg should be assessed regarding its overall alignment. Bilateral long-leg-radiographs allow values of mechanical and anatomical axis to be compared with the other leg. If significant mal-alignment is discovered and the patient presents with a thrust movement during walking, re-alignment osteotomy should be considered. In patients with POSTERO-LATERAL ROTATORY INSTABILITY (PLRI) a high tibial valus osteotomy might be sufficient to cure the patient's symptoms and, henceforth should be contemplated as a primary procedure before considering ligament reconstruction.
The following broad surgical options are available:
1. Re-attachment of avulsed ligaments
2. Repair of ruptured ligaments
3. Reinforcement of ruptured or stretched ligaments
4. Reconstruction of a torn or incompetent ligament by means of autografts or allografts
5. LONG TERM PROBLEMS
We know that untreated ligament injuries invariably lead to the development of degenerative changes within the knee. This process may take several decades but in severe cases such problems may be apparent as early as three to four years after injury. The process is compounded if the patient has also sustained damage to the meniscus. Meniscal tears may occur at the time of injury or thereafter and to some extend dependant on the degree of knee laxity.
Ligament reconstruction, however, does not guarantee to protect the knee from degenerative changes and recent studies from Australia have shown that 60% of all patients undergoing ACL reconstruction will have develop some radiographic signs of early degenerative joint changes at 6 years post surgery. Patients with previous meniscal damage are likely to do worse. This does however not indicate that patients are necessarily symptomatic at such a stage and in the cited study most patients were free of symptoms. This observation highlights that surgery will reduce joint laxity and abolish instability feelings but may not alter the natural history of increased likelihood to develop degeneration after ligament injury.
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Radiographs of patients who underwent ligament reconstruction with extra-articular tenodesis (left) and intra-articular ACL reconstruction (right). Both patients suffered significant joint degeneration approximately 18 years post surgery.
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