First of all, when is meant by a locked knee? Locked knee is the sensation of the knee suddenly getting jammed, or stuck in a certain position. The affected knee cannot be straightened or bent. One might need to either force the knee straight or twist it in certain positions to “unlock” it, often causing more pain and swelling.
Common causes of “locked knee” include displaced meniscus tear, osteochondral fragments, loose bodies, ruptured ACL stump getting in the way. Sometimes severe muscle spasms around the knee, particularly muscles around the back of the knee, can give rise to the sensation of a locked knee. However this is not a true “locked knee” as there are no mechanical obstructions within the knee that impedes its normal movement. Importantly, oral muscle relaxants and anti-inflammatory medications can alleviate muscle spasms which would then resolve this pseudo ‘locked knee”. I will discuss more in detail on the three most common causes of true locked knee below.
The three most common causes of true locked knee
1. Meniscus tear
Meniscus or menisci (plural) are C-shaped fibrocartilaginous structures within the knee joint. There are two of them in every knee; one on the inner (or medial) side, another on the outer (or lateral) side of the knee. They act as shock absorbers and distribute stresses across the knee joint, thus protecting the cartilage which coats the surfaces within the knee joint. They can be torn or damaged during a sudden awkward twisting force to the knee, or they can tear as part of the process of ageing. In sudden traumatic sporting injuries, meniscus tears are commonly associated with ligamentous injuries for eg anterior cruciate ligament tear. In the elderly age group, degenerative type of tears are more common.
Small isolated undisplaced meniscus tears can be treated non-surgically, with rest, anti-inflammatory medications in the acute phase and physiotherapy once pain subsides. Large unstable tears especially those which cause locking symptoms should be treated surgically rather than to continue physical activities. The reason is that continuing sports with a displaced unstable meniscus tear can cause injury to the surrounding cartilage, which may then be harder to treat, with poorer long-term outcomes.
Surgical treatment of meniscus tears is done arthroscopically. This means that the surgeon will make two small about 1cm long incisions on either side of the knee joint. Fluid is then gently pumped into the knee to wash out any debris and also to help with visualisation. An arthroscope (a camera system with lens at the end) is then inserted into the knee to inspect the structures within. Specialised tools which can include shavers, arthroscopic punches and radiofrequency wands are then used to clean up the knee. Meniscus tears are then trimmed or edges freshened up in preparation for repair. Specialised suture are then inserted via the small wounds to stitch up the tears. Sometimes the tear may occur in areas where there is less blood supply, or deemed not repairable. In such cases, the tears are trimmed back so that those flaps would not block the knee and cause pain.
2. Loose bodies
3. Osteochondral fragments
Osteochondral fragments can arise from conditions such as Osteochondritis Dissecans, or from traumatic injuries to the knee which knocks off a fragment of cartilage with its underlying bone. Osteochondritis Dissecans is a condition which occurs usually in adolescence. It is commonly believed that this is due to abnormal blood supply to the underlying bone, which results in detachment of a fragment of bone with its attached cartilage. It is rather uncommon, though it is certainly something that one does not want to miss or delay treatment, as this would affect the long-term outcome of this disease.
Clinical Evaluation of a Locked Knee
If you have symptoms of locking, you should seek an evaluation. Your doctor will take a history and examine your knee. Where necessary, additional investigations may be performed to understand the cause of your locked knee. Once we have established the cause of your symptoms, we will explain the treatment plan. Where surgery is necessary, we will detail the surgical plan and the expected recovery process after surgery. Ask questions, clarify your concerns, and take time to decide.
At Hip and Knee Orthopaedics, we believe that every patient deserves to receive comprehensive and efficient care for their musculoskeletal conditions so that they can gain back their independence in mobility and enjoy quality time with their loved ones.
With a passion for treating hip and knee conditions, orthopaedic surgeon Singapore
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