Pertinent Insights On Treating Second MPJ Pathology
A wide range of pathologies can arise at the second MPJ, making an accurate diagnosis vital. Accordingly, these authors offer diagnostic insights, a guide to conservative and surgical treatment options, and an intriguing case study.
Understanding second metatarsophalangeal joint (MPJ) pathology, a comprehensive term that includes multiple pathological entities, requires the ability to identify and discern particular clinical attributes associated with each condition. A variety of pathologies arise at this anatomic location. A few of these pathologies include synovitis, plantar plate tears, osteochondritis dissecans and crossover toe deformities.
As with any initial workup, a thorough history is important to understand whether the condition is acquired, idiopathic, traumatic, congenital or progressive. Understanding and identifying the appropriate etiology is imperative in order to establish an effective treatment plan.
The physical exam must start with a general assessment of the lower extremity. A detailed biomechanical exam helps identify lower extremity structural and soft tissue deformities that can be contributing factors in the development of second MPJ pathologies. Genu varum, genu valgum, equinus contracture and dropfoot are all clinical abnormalities that one should evaluate during the initial physical assessment. Pedal examination should include an inspection for presence of callosities indicative of sub-second metatarsal head pressure, hammering of the digits, hallux valgus deformity, edema, ecchymosis or widening of the gap between web spaces (Sullivan’s sign).
Additional clinical tests include palpation of the affected area to isolate the location of pain as well as evaluation of the joint as it goes through range of motion. The Lachman vertical stress test is a specific exam that is available to evaluate joint instability and assess the integrity of the plantar plate and periarticular structures. Pain that occurs with the dorsal-plantar translational stress during this test can be indicative of plantar plate attenuation. Pain with passive range of motion within the joint can signify synovitis, capsulitis or cartilage defects.
Evaluating the first ray is also critical when trying to determine the etiology of second MPJ pain as there are various underlying conditions at this location that can cause second MPJ pathologies. Hallux abductovalgus, hallux rigidus, first ray hypermobility and metatarsus primus elevatus have the ability to cause an imbalance in the forefoot contributing to overloading of the second MPJ. Additionally, an equinus deformity may be a potential contributing cause of forefoot and specifically second MPJ overload. These conditions all cause a biomechanical shift of the plantar pressures to the area beneath the second metatarsal head and joint, causing increased loading and strain to the joint and periarticular structures.
With hallux valgus deformities, the deviated hallux can allocate the space occupied by the second toe, causing the lesser toe to contract dorsally and deviate medially over time.1 Researchers have demonstrated that increased second metatarsal length is a factor in the development of second MPJ instability with increased plantar plate pressures and medial deviation of the second toe as a result of the attenuation of plantar structures.2
In addition, hypermobility of the first ray places a large amount of pressure on the second metatarsophalangeal joint complex. Though no standard device can determine hypermobility at this location, one effective clinical technique includes dorsiflexion of the hallux to engage the windlass mechanism while stabilizing the lateral forefoot and manually mobilizing the first metatarsocuneiform joint in the sagittal plane and observing for excessive motion.