Anterior Knee Pain
Anterior knee pain is one of the most common conditions that bring both young and old patients to musculoskeletal medicine clinics.
The differential is extensive and includes the patella-femoral joint (PFJ), the patella tendon, the Hoffa’s fat pad, isolated bursitis, Plica syndromes, traction apophysitis in adolescents (Osgood-Schlatter), and intraarticular causes. For the sake of this patient information context, we will be focusing specifically on the most common causes, which are the PFJ and the patella tendon. For other differentials more information can be found here: Narrative: Review of Anterior Knee Pain Differential Diagnosis (Other than Patellofemoral Pain) – PMC
The annual prevalence PFJ pain in the general population is 22% Incidence and prevalence of patellofemoral pain: A systematic review and meta-analysis | PLOS One, patella tendinopathy is less common in the general population but with prevalence rates varying from 11-45% for athletes Patellar tendinopathy: an overview of prevalence, risk factors, screening, diagnosis, treatment and prevention – PMC
The exact pathophysiology of PFJ pain is still widely debated but has been attributed to simple overload in the majority of cases, leading to the loss of normal tissue homeostasis. An inflamed synovial lining and increased intraosseous pressure of the patella have all been documented as contributing to the perception of anterior knee pain. The pathophysiology of patellofemoral pain: a tissue homeostasis perspective – PubMed. Osteoarthritis is a cause of PFJ pain, please see our osteoarthritis knee page for more information.
Patella tendinopathy is an overuse injury of the extensor mechanism of the knee. It is often seen in athletes with high-end/high-demand sporting activities that require a lot of jumping and ballistic movements. This tendon goes through the same pathophysiological changes as any other tendon in the body: ‘degeneration within the tendon itself with disorganisation of the collagen fibres and an increase in the microvasculature and sensory nerve innervation’ Tendinopathy – PubMed. This ultimately leads to pain and subsequent loss of performance for the individual.
What are the signs and symptoms?
As the name suggests, in both conditions pain is felt in the anterior knee. With PFJ pain, the pain is poorly localised around the kneecap; it is typically aggravated by squatting, running downhill and descending stairs. There may be some associated crepitus reported by the patient or reproducible on examination. Overview: Patellofemoral pain syndrome (runner’s knee) – InformedHealth.org – NCBI Bookshelf. An axial (compressive) load through the Patella femoral joint will often provoke symptoms, though the diagnostic value of this is debated The diagnostic value of the Clarke sign in assessing chondromalacia patella – PubMed.
With patella tendinopathy there are often key differences both subjectively and objectively. Pain from the patella tendon is normally quite accurately isolated. Symptoms are usually localised to the inferior pole of the patella or, less commonly, at the insertion onto the tibial tuberosity. Palpation of these bony landmarks often provokes symptoms. Patients typically describe activity-related anterior knee pain that is worse initially on starting activity, eases as sessions develop, only to return following cessation. As the disease progresses symptoms often become more persistent even at rest. Patellar tendinopathy: an overview of prevalence, risk factors, screening, diagnosis, treatment and prevention – PMC
How is it diagnosed?
The diagnosis will be made from a combination of your clinical history and examination findings and, in certain cases, confirmed with imaging.
In the main part, PFJ pain and patella tendinosis are both clinical diagnoses, meaning if you have typical symptoms, imaging is not initially required. It is important to remember that for the majority of PFJ pain, there are no radiographic causes evident. However, for symptoms that are refractory to initial management, plain Film X-rays can assess for any evidence of arthrosis in the patellofemoral joint. They can also assess the alignment of the patella and the morphology of the trochlea groove to make these articulations have good congruency. Radiologic Assessment of Patellofemoral Pain in the Athlete – PMC
Ultrasound can be helpful at viewing the patella tendon, seeing the severity of tendinopathy, as well as excluding other potential causes of patella tendon pain, including tendon tears and bursitis. Though imaging often demonstrates a combination of these pathological changes. It has advantages over MRI given its dynamic capabilities and higher spatial resolution Musculoskeletal Ultrasound: An Essential Tool in Diagnosing Patellar Tendon Injuries – PMC making it often the first-line imaging modality to assess for pathology of the extensor tendon.
MRI has the advantage of assessing both the PFJ and patella tendon. It is the imaging of choice in traumatic cases of patellofemoral dislocation or subluxation to assess for osteochondral injuries and disruption to the medial patella-femoral ligament, helping guide surgical management Radiologic Assessment of Patellofemoral Pain in the Athlete – PMC.
How is it treated?
Treatment options are divided into conservative and surgical.
Conservative options:
- Physiotherapy is the gold standard treatment and the first-line management in both cases. They will be able to address any biomechanical issues that may be contributing to your PFJ symptoms. Effectiveness of therapeutic physical exercise in the treatment of patellofemoral pain syndrome: a systematic review – PMC. For patella tendon pain, the aim of physiotherapy is to improve the tolerance and capacity of the extensor compartment of the knee through a graded and progressive rehab plan. Effectiveness of progressive tendon-loading exercise therapy in patients with patellar tendinopathy: a randomised clinical trial – PubMed.
- For refractory cases that are struggling to progressive with rehab, ultrasound-guided ‘high volume’ injections can be utilised in the management of patella tendinopathy. This process involves injecting local anaesthetic, saline and a small amount of steroid into the interface between the patella tendon and Hoffa’s fat pad to mechanically disrupt neovascularisation (new blood vessels) and nerve ingrowth. These changes can be visualised on ultrasound and targeted dynamically. High-Volume Image-Guided Injection for Recalcitrant Patellar Tendinopathy in Athletes – PubMed
- PRP injections. A further injectable option for patients with patella tendinopathy +/- associated small tears is a PRP injection into the tendon itself under ultrasound guidance. The aim is to promote healing and reduce inflammation allowing better compliance with rehab. Its efficacy remains in debate as there remains no clear consensus on optimal dose and number of injections required to enhance its efficacy Platelet-rich plasma for jumper’s knee: a comprehensive review of efficacy, protocols, and future directions – PubMed), but it has been shown to be beneficial it carefully selected patients Platelet-rich plasma for patellar tendinopathy: a randomized controlled trial correlating clinical outcomes and quantitative imaging – PubMed
- For patients with PFJ pain that are refractory to initial management, a hyaluronic acid injection may be beneficial The role of viscosupplementation in patellar chondropathy – PMC. There is typically a better response in patients with degenerative change in their PFJ. Steroid injections in this cohort of patients can also be helpful at breaking a repeating pain cycle allowing better compliance with rehab.
Surgical options:
For patellar tendinopathy surgical input is typically the last resort, saved for those with severe and refractory symptoms despite extensive conservative management.
- There are both arthroscopic and open techniques to address the tendon itself. Debridement (removing damaged tissue) is the most common surgical option. Bone or tendon resection at the inferior patella pole and tendon repair are also options depending on the exact cause of your symptoms. The efficacy of surgical management for patella tendinopathy is generally unclear but has been shown to be beneficial in patients that have failed conservative options, allowing a high return to play. A Systematic Review of Surgical Treatment for Refractory Patellar Tendinopathy – PMC
For patients with isolated PFJ pain that is refractory to conservative management or for patients with repeated patella dislocations, surgery is aimed at addressing the underlying aetiology.
- Surgical treatment for PFJ arthrosis is achieved with either PFJ or a full knee arthroplasty. Should we recommend patellofemoral arthroplasties to patients? a systematic review – PMC. For recurrent dislocations, surgery may include a repair of the medial patella-femoral ligament, lateral release and/or trochleoplasty Medial Patellofemoral Reconstruction Techniques for Patellar Instability – PubMed.
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