Arthrofibrosis may be limited to one anatomic area or involve the entire knee joint, including the extra-articular tissues that surround the joint.
In this portion of the course. I will describe the generalised condition so that future discussions of surgical and non-surgical options can be put into better context.
In part 5, I do note that arthrofibrosis can become established as early as 6 weeks postop, but I think one has to be cautious in providing a more definitive statement. I don't want to alarm people unnecessarily, and certainly the time factor varies tremendously from case to case. Even the word 'established' can be interpreted differently - established vs. permanent vs. still treatable.
Adhesions inside the joint spaces
The knee is frequently swollen in the first two weeks after injury or surgery. This may be due to blood within the joint from torn blood vessels (haemarthrosis) or from a general effusion from the irritated joint lining or synovium.
During this phase one may have:
The joint normally copes with small amounts of blood by breaking it down and reabsorbing its components. In a similar manner, an effusion is normally reabsorbed and the swelling diminishes. In cases in which arthrofibrosis develops, the swelling may persist. If the haemarthrosis is too large for the joint to resorb, it may itself cause irritation and set off the arthrofibrosis cascade. The irritated joint lining produces more fluid which becomes thick and sticky, forming gummy adhesions stretching across the joint spaces.
Initially these adhesions are easily broken by knee flexion and extension exercises. However, if the joint is painful, the quadriceps muscles inhibited, the knee tense with fluid, or if the knee has been immobilised, then joint motion does not occur and adhesions begin to thicken and change in character.
The suprapatellar, medial, and lateral capsular pouches (see Part 3) are the soft tissue spaces generally first affected. This tends to limit knee flexion and tether the patella, reducing patellar mobility both from side-to-side (medial-lateral) and up-and-down (superior-inferior) directions. This is a crucial point to note - if the physical therapist finds that the affected patella has become limited in mobility compared to the normal knee, then the clinical team should be alerted to the likelihood of the establishment of adhesions in the soft tissue spaces surrounding the patella.
Rehab/surgical options relevant at this stage (these will be discussed in the next part of the course)
proceeding to -
- for limitation of extension - extension overpressure programme, serial extension casting, posterior night splints
- for limitation of flexion - overpressure flexion program, gentle MUA (manipulation of the joint under anaesthesia), insufflation (expanding the joint space with saline), arthroscopic lysis of adhesions (maybe with epidural continuing into postop period)
Exuberant fibrosis affecting joint structures and obliteration of synovial pouches
If adhesions are not recognised and adequate therapy undertaken to break these filmy strands, then the more dangerous second phase may begin. The adhesions start to turn into scar tissue, a process known as 'fibrosis'. Scar tissue cells (fibrocytes) become apparent within the adhesions, the filaments thicken and become fibrous, and the two sides of the suprapatellar pouch and the medial and lateral capsular pouches become drawn together - obliterating these very important anatomical soft tissue spaces.
The fat pad which lies below the patella becomes involved. Normally, the fat pad is a soft mobile structure which touches but does not attach to the patella and meniscus. However, fibrosis in the fat pad turns it into a thickened structure, welding it to the patella, the anterior horn of the meniscus, and the intermeniscal ligament.
The fibrocytes proliferate and the fibrotic tissue spreads onto the cruciate ligaments and welds them together. Scar tissue can bunch up in the intercondylar notch of the femur to form a lump known as a cyclops lesion. This will lead to problems with knee extension and a clunk may be experienced as the knee is extended.
Rehab/surgical options relevant at this stage (these will be discussed in a later part of the course)
- anterior interval release (mini-arthrotomy)
- arthroscopic debridement
- open debridement
- aggressive postop rehab with epidural, professional pain management, CPM (continuous passive motion), extension splinting
Scar tissue contraction and consequences outside the joint
In the most aggressive form of arthrofibrosis, the inflammatory process involves other soft tissue spaces, especially around the patellar tendon and the deep infrapatellar bursa.
A 1-cm wide extra-capsular band of scar tissue often develops in the midline that extends obliquely from the top of the patella to the front of the femur in the space between the suprapatellar pouch and the undersurface of the quadriceps muscles (outside the capsule of the knee). This band of scar tissue may be responsible for the development of a distinct 'clunk' the patient experiences with knee motion.
The scar tissue now matures further and undergoes a 'contraction' phase. Scar tissue in the fat pad contracts which can become nipped and painful with joint movement.
The capsule around the joint may also begin to thicken. The fibrous process spreads to the capsule toward the back of the knee (postero-medial and postero-lateral capsule). The capsule contracts, obliterating its normal folds which usually exist to facilitate joint movement.
The muscles may also become affected. The tendons of the hamstrings muscle may contract which pulls the joint into further flexion and prevents knee extension. The patellar tendon may contract and pull the patella downward into an abnormal position known as 'patella infera'. There is now loss of both knee flexion and extension with a 'hard end point'.
The muscles around the joint may also become involved in a process known as 'myositis ossificans' where bony material is laid down within the muscle.
Salvage options relevant at this stage (these will be discussed in a later part of the course)
- posterior capsular release
- excision of myositis ossificans