Knee, the largest joint in our body, is an important weight-bearing joint during standing, walking, running, bending, and lifting objects. The knee joint has strong ligaments for stability and muscles for powerful movement. The joint is formed by thigh bone (femur), two bones of the leg (tibia and fibula), and the knee cap (patella). It has three compartments – inner (medial), outer (lateral), and front (patellofemoral). Two ligaments (cruciate) incorporated inside the joint hold the bones together. Two more strong ligaments are placed on either side of the knee. A piece of cartilage (meniscus) intervenes between the femur and tibia. The rubbery meniscus acts as a shock absorber and allows unrestricted movement of bones over each other. A dozen bursas (fluid-filled sacs) are placed around the knee that enable free sliding of muscles and tendons during movements at the knee joint. Quadriceps and hamstrings are powerful muscles placed in the front and back of the thigh, respectively. Quadriceps muscles straighten the knee, whereas hamstrings bend the knee and straighten the thigh. Quadriceps muscles narrow down near the knee to form a tendon and ligament, which hold the knee cap in place and stabilize the knee on the front side. The load-bearing axis of the knee is in a line that runs from hip to ankle. Climbing puts 3-4 times body weight stress, whereas squatting places about eight times body weight stress on the knees. Abnormal knee alignments (bow-legs, knock knees) increase the risk of osteoarthritis.
Improper use of muscles and overload during movement or exercise leads to knee dysfunction and pain. Hip disease, malalignment of the patella, and foot abnormalities (e.g., flat feet) can also cause abnormal stress and knee dysfunction. Knee pain may be associated with other symptoms such as 'giving way' or buckling, clicking or crackling sound, and locking. Pain originating from structures around the knee is generally localized to a specific area and does not restrict passive movements.
Injuries of knee ligaments are quite common during sports. Pain starts immediately after the injury but may be difficult to localize. Collateral ligament injuries cause pain on either side of the knee. In contrast, cruciate ligament injury is felt deep inside the knee. Pain is present even at rest and worsened by bending of the knee, standing, and walking. The knee may be swollen and warm. Ligament injuries are initially treated with rest, immobilization, and pain killers. An orthopedic consult must be sought at the earliest. Sudden twisting of the knee while bearing weight can lead to meniscus injuries. Though common in sports injuries, meniscal tears have a higher incidence in the elderly due to aging cartilage. Mechanical symptoms such as locking, buckling, and popping sensation during certain activities are common in meniscal injury. Swelling may or may not be present. Routine X-ray may not be sufficient for the diagnosis of ligament of meniscus injury. MRI scan or arthroscopy may be required in these cases.
Some important conditions causing pain in the knee region are as follows:
- Baker's Cyst: This is a swelling on the back of the knee that is usually painless and resolves on its own. A large cyst may cause some discomfort and restriction of movements. This bulge is filled with excessive joint fluid and can rupture, leading to severe pain and swelling in the calves. No treatment is usually necessary for small painless cysts except managing the underlying cause, such as arthritis. Large cysts may need needle aspiration along with an injection of glucocorticoid (steroid). Surgical removal is rarely required.
- Prepatellar Bursitis: Prepatellar bursa overlies patella. It can swell and be painful due to repeated trauma or strain during occupational overuse (e.g., housemaids, clergypersons, roofers, carpet-layers) and can also follow an injury. Warmth and redness may also be associated. However, it does not limit joint movements. Treatment consists of rest, ice compresses, and pain medications. Needle aspiration and injection of steroid may be required in some cases. Septic bursitis warrants fluid examination and a suitable antibiotic. Surgical removal of bursa may be needed in septic cases.
- Anserine Bursitis: This bursitis causes pain on the inner side lower knee (upper end of the shin bone). More common in obese middle-aged females, this condition leads to pain while climbing or descending stairs. Treatment is similar to prepatellar bursitis.
- Infrapatellar Bursitis: Infrapatellar bursa is located beneath the patella under the patellar ligament. Bursitis is usually associated with swelling of the adjacent patellar tendon due to jumping injury (jumper's knee). Treatment is similar to that of prepatellar bursitis.
- Suprapatellar Bursitis: The suprapatellar bursa is located above the patella behind the Quadriceps tendon. It is an extension of the knee joint and can swell with knee effusions. Swelling of the suprapatellar bursa causes pain and restriction in this region. Moreover, puncture wounds in this region can lead to bleeding and sepsis in the knee joint. Treatment is similar to that for other bursae.
- Chondromalacia patellae: This is due to the weakening and softening of cartilage beneath the patella leading to discomfort and tightness in the front of the knee. It is more common in women. Knee (knock knees) or foot (flat feet) malalignment predisposes to the development of chondromalacia patellae. The pain is aggravated by folding knees and by activities such as running and jumping. Chronic pain restricts the movement of the knee and leads to weakness of thigh muscles. Initial treatment consists of rest, ice packs, and pain killers. Avoid activities that cause knee pain. Supervised physical therapy is essential for recovery. Fortunately, full recovery is possible, although this may require several months or years. Weight reduction hastens recovery from knee pain. Chondromalacia patellae of childhood usually resolves totally in adulthood.
- Osgood-Schlatter disease: This is swelling of the bony attachment of the patellar ligament to the upper end of the shin bone. It is commonly observed in enthusiastic young athletes involved in sports with running or jumping activities (e.g., football). Muscle tendons are stronger than bone in this age group. Pain and swelling at the upper end of the shin bone are felt during climbing upstairs and worsens with sports. Rest (and sometimes immobilization), ice packs, and pain killers are the initial treatment of choice. Later, this should be followed by quadriceps strengthening exercises. Most cases will resolve spontaneously when bone growth stops. A few refractory patients may require surgical treatment.
- Iliotibial Band Syndrome: A thick and strong fibrous band extends from pelvic bone to the upper end of the shin bone on the outer side of the thigh. Iliotibial band syndrome (ITBS) is an overuse friction injury commonly seen in runners, cyclists, and military personnel. Pain is localized on the outer and upper side of the knee and aggravated by walking (painless to start with) and running downhill. Pain may extend to the hip along the fibrous band that can be tender. Running must be stopped immediately. Rest, icepacks, painkillers, and physiotherapy are successful in most patients. Surgery is rarely indicated and may be contemplated if pain persists for more than 6-9 months despite adequate physical therapy.