Soft tissue knee injuries

Sam, a 12-year-old boy, presents to your department after a soccer blitz. He was tackled, heard a pop, and now can’t bear weight on his right knee.

As the popularity and intensity of children’s sports increase, increased demands are placed on children and adolescents. This has resulted in an increased presentation of children like Sam. They can present with knee pain that is traumatic or atraumatic, acute or chronic. Paediatric patients are particularly vulnerable to overuse injuries involving the physes and apophyses due to their inherent weakness.

Along with these, there has also been an increase in soft tissue injuries. These are seen more commonly in older children/adolescents as their bones become stronger and are less likely to fracture with age.

History/Examination

Important points to note on the history include:

• If there was a clear onset of pain
• Traumatic or atraumatic
• Duration of pain
• Previous injury/surgery
• Site of the pain (try to be as specific as possible)
• Severity of pain
• Nocturnal pain
• Systemic symptoms
• Associated swelling (intermittent or progressive)
• Contralateral injuries (may result in abnormal gait placing additional pressure on knee)
• Hip or back pain

Recalling the anatomy of the knee makes evaluating the site of pain easier.  The following make up the knee; all can be injured/inflamed and cause pain.

1. Bones around the knee – femur ends at lateral and medial condyles, which articulate with the tibial plateau and anteriorly the patella unsheathed in the patellar tendon.
2. Ligaments – anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial and lateral collateral ligaments.
3. Meniscus – medial and lateral menisci act as shock absorbers and interdigitate into the ACL and PCL for more stability.
4. Bursae – supra-patellar bursa, infra-patellar bursa, pre-patellar bursa, and pes anserine bursa (medial aspect of knee).
5. Tendons – quadriceps tendon (inserts into patella), patellar tendon (inserts into tibial tuberosity)
6. Other – iliotibial band (fibrous support of fascia lata originating at the external lip of iliac crest and inserting into the lateral condyle of the tibia).

Examination in the acute setting is often difficult and may be limited. This is due to swelling, pain and anxiety. Try your best to be as detailed as possible but ensure you note any red flags on examination. These are:

• Inability to do straight leg raise (extensor mechanism rupture)
• Ligamentous laxity
• Catching, locking or giving away (meniscal injury)
• Inability to fully straighten the knee

After a thorough history and examination, you discover he was tackled, and the other player’s foot landed on the lateral aspect of his knee. On examination, you find swelling on the medial aspect of the knee and laxity of the medial collateral ligament when valgus stress is placed on the right knee.  You clinically diagnose a medial collateral ligament injury. He is placed in a brace and referred to an orthopaedic clinic.

Injured ligaments are considered “sprains” and are graded on a severity scale.

• Grade 1 sprains: The ligament is mildly damaged. It has been slightly stretched but can still help keep the knee joint stable.
• Grade 2 sprains: The ligament has been stretched to the point where it becomes loose. This is often referred to as a partial tear of the ligament.
• Grade 3 sprains: This type of sprain is commonly called a complete ligament tear. The ligament has been split into two pieces, and the knee joint is unstable.

Ligament specific examinations:

• Anterior and posterior drawer tests – asses anterior and posterior cruciate ligament integrity.
• Lachman test – assesses ACL integrity. Most sensitive test for ACL rupture. Non-dominant hand cups and support the knee. Ensure quads and hip flexors are relaxed for it to work. The dominant hand grasps the proximal tibia, knee flexed at 20-30 degrees. Pull sharply. Tibia shouldn’t move much and should have distinct endpoints.

• Posterior sag test – patient supine, hip flexed at 45 degrees and knee at 90 degrees. Look at the knee from the lateral position. If PCL is damaged you’ll see tibia sagging posteriorly.
• Varus and valgus stresses – assess integrity of medial and lateral collateral ligaments. Compare both sides for laxity.

Management of MSK knee injuries

• Unstable joints require a thorough examination of neurovascular status, orthopaedic consultation and close follow-up.
• ACL tears often have poor healing abilities and may require surgical repair if the injury is significant.
• PCL is much better at healing than the ACL and low-grade tears are managed non-operatively, with grade 3 or higher needing reconstruction.
• Collateral ligament injuries have good healing potential, so rest, ice, bracing and slow advancement of a range of motion is the management primarily undertaken.

A short while later, one of Sam’s team-mates, Patrick, presents to ED. He was also playing in the soccer blitz. He got sudden knee pain when turning, and his knee is now locked. Following assessment, you suspect a meniscal injury.

Meniscal injuries

Meniscal injuries can be traumatic or atraumatic. Suspect if the knee is locked, there was a twisting mechanism, a tearing sensation, or an effusion.

Specific examinations include:

• McMurray test – patient supine, hip and knee flexed at 90 degrees. Non-dominant hand placed over joint line. The dominant hand grasps the patient’s heel and internally and externally rotates the tibia, exerting valgus and varus forces while extending the leg. This helps to grind on either the medial or lateral menisci. Pain, popping or clicking is a positive test.
• Appley compression test – the patient lies prone with the knee bent 90 degrees. The examiner rotates the leg externally and internally under simultaneous vertical pressure. A painful pop can point to a meniscal injury.

Treatment includes physiotherapy to compensate for the tear but surgical management may ultimately be required. Follow-up with orthopaedics is required.

Patrick’s sister was also brought for review. She is 15 years old and has had intermittent knee pain for the last few months, but it gets much worse after she plays sports. She also says it hurt her after the cinema yesterday. You suspect patellofemoral pain syndrome.

Patellofemoral pain syndrome (PFPS)

The pain is frequently described as anterior but is often poorly localised. It may feel like it’s “under” or “around” the patella. Pain is classically exacerbated by prolonged periods of sitting, use of stairs and squatting (theatre sign). Pain may be present for several weeks, exacerbated by activity and relieved after periods of rest. Often there is a deterioration in sports performance or inability to participate prompts patients to seek medical review.

Clinical examination should look for gait abnormalities, increased lumbar lordosis, and any asymmetry in the hips or lower extremity. It is not uncommon to have reduced flexibility in the hamstrings or quadriceps.

Clarkes sign – positive in PFPS. Patient supine, knee extended. Grab the superior pole to the patella with a thumb and index finger and have the patient activate the quadriceps while you inhibit the patellar movement. This causes grinding of the articular surface between the patella and femur. Pain is indicative of PFPS.

Investigations are not routinely required. However, knee radiographs may assist in ruling out other conditions such as osteochondritis dissecans of the knee/patella and stress fractures of the patella. Radiographic imaging in PFPS is not diagnostic. It is necessary to combine any findings with your clinical examination.

Management of this is conservative as it is a self-resolving condition. It typically resolves over weeks to months but has been known to take up to two years for the resolution of symptoms. Management involves reducing activity (complete cessation usually not required), ice, rest, anti-inflammatory for pain control (short-term use), avoidance of aggravating exercises (e.g. squatting), and some find relief with taping/knee-braces. Exercises that strengthen and increase flexibility of the quadriceps, hamstrings, soleus and gastrocnemius muscles are also recommended.

What else can cause non-specific knee pain?

• Ask the patient to tighten knee and palpate the quadriceps tendon at superior pole (tenderness indicates possible tendonitis), straight leg raise (assessing quadriceps strength and integrity).
• Palpate body of patella for tenderness (Sinding-Larsen syndrome) and then patellar tendon and tibial tuberosity (Osgood-Schlatter syndrome).
• Palpate the medial side of patella (possible inflamed medial plica band) and also palpate the proximal tibial surface (medial anserine bursa- pain, swelling, tenderness may indicate bursitis).
• Feel under the patella (tenderness on articular surface could indicate patella-femoral syndrome).
• Lateral – assess for patellar instability (need quadriceps relaxed and knee flexed at 30 degrees). Apprehension indicates patellar laxity and potentially previous dislocation.
• Joint line – bend the knee and palpate either side slowly and carefully. Try to localize as much as possible. Tenderness may indicate a meniscal tear.
• Hamstring muscles: With the knee flexed palpate the hamstring muscles. Laterally is the biceps femoris and medially semi-tendinosus and semi-membranosus. Chronic tightness may be the cause of knee pain.
• Patellar ballottement- effusion

Bottom line

A thorough history and examination can greatly assist in reaching the diagnosis. A correct diagnosis helps to properly counsel patients and appropriately manage their expectations. Without proper treatment, knee injuries can lead to chronic knee problems, early-onset arthritis, injury to surrounding tissues, and prolonged healing times. Missed injuries can also cause recurrent cartilage damage, instability in the knee, and unnecessary time away from physical activity. It is our duty to diagnose these injuries in a timely manner and provide appropriate advice, support and follow up.

Below is a useful table outlining the causes of intrinsic knee pain, separated by site of pain on examination (table 1).

References

Beck NA, Patel NM, Ganley TJ. The pediatric knee: Current concepts in sports medicine. J Pediatr Orthop Part B. 2014. doi:10.1097/BPB.0b013e3283655c94.

Brooke Pengel K. Common overuse injuries in the young athlete. Pediatr Ann. 2014;

Finlayson C. Knee injuries in the young athlete. Pediatr Ann. 2014;

Calmbach WL, Hutchens M. Evaluation of patients presenting with knee pain. Part II Am Physician. 2003.

PEM Playbook Knee Pain podcast https://pemplaybook.org/podcast/knee-pain/