Case Notes: Varus instability of the hallux interphalangeal joint in a taekwondo athlete

Case Summary

• A 19-year-old female taekwondo athlete presented with pain and instability of the hallux interphalangeal (IP) joint in the left foot after repeatedly spraining the big toe during rapid foot raises for kicks. The toe was caught on the mat, leading to varus instability of the IP joint.
• Clinical finding: the hallux IP joint was unstable and easily subluxed medially with tenderness on the lateral side; dorsal and plantar aspects were non-tender.
• Imaging:
  • Radiographs showed no structural abnormality.
  • Varus stress radiographs demonstrated a marked widening of the lateral joint space on the left IP joint compared with the contralateral foot (Figure 1).
• Initial management: buddy taping of the first and second toes was ineffective; patient needed a stable joint to resume training.
• Treatment plan: repair of the collateral ligament was deemed unlikely due to chronicity; planned reconstruction of the lateral collateral ligament of the hallux IP joint using a tendon graft.
• Surgical procedure (summary): lateral longitudinal incision over the IP joint; assessment showed the middle portion of the collateral ligaments had healed with scar tissue insufficient for repair or plication; drill holes were made parallel to the joint at normal insertion sites; a palmaris longus tendon graft was harvested from the forearm and passed through the drilled holes; ends were tied medially after confirming full ROM.
• Postoperative course:
  • Immobilisation for 4 weeks.
  • Active ROM begun thereafter; full return to training at 3 months.
  • At 12 months, patient asymptomatic, IP joint stable and congruent, with 45° of flexion and full extension in the operated toe, compared with the unoperated toe which had 60° of flexion (Figure 5).
• Outcome: successful reconstruction with a stable and mobile IP joint permitting continued training; no residual varus instability at 12 months.

Anatomy and Biomechanics of the Hallux IP Joint

• The hallux IP joint is a simple hinge joint allowing sagittal plane motion and is inherently stable in the transverse (varus–valgus) plane compared with the metatarsophalangeal (MTP) joint.
• Key stabilizers in the transverse plane:
  • Collateral ligaments: attach to the lateral side of the proximal phalangeal head and the dorsal tubercle at the base of the distal phalanx; provide static stability.
  • Lateral collateral ligament and its normal insertion sites are critical for varus stability.
• Sagittal plane stability is provided by:
  • Joint capsule, thickened fibrocartilaginous plantar plate, and the flexor and extensor hallucis longus tendons.
• The joint geometry contributes to stability:
  • Bicondylar shape and the short lever arm of the distal phalanx help maintain stability.
• Mechanism of injury in general:
  • Hyperextension can cause a traumatic dorsal dislocation; closed reduction is usually straightforward unless plantar plate incarceration or associated fragments prevent reduction.
  • In transverse-plane trauma (e.g., stubbing the toe on a stair or rock), intra-articular fractures are more common than pure ligament ruptures due to strong collateral ligaments and stability.
• Surgical rationale in this case:
  • Reconstruction chosen over arthrodesis to preserve joint mobility essential for push-off in a martial arts context.

Mechanism of Injury and Injury Patterns

• Forefoot injuries are common in sports involving running, jumping, or contact, frequently around the MTP joint (e.g., collateral ligament rupture, turf toe, sesamoid pathology, metatarsal stress fracture).
• The hallux IP joint, being a hinge joint, is generally stable in the transverse plane and has received less attention in athletic injuries compared with the MTP joint.
• In this case, varus instability likely resulted from transverse-plane force (e.g., kicking action) with repetitive sprains, leading to chronic laxity or deficiency of the lateral collateral ligament.

Diagnosis and Imaging Findings

• Diagnosis relies on clinical instability and imaging findings.
• Radiographs:
  • No structural abnormality detected on standard views.
• Stress radiographs:
  • Demonstrated marked widening of the lateral joint space on the left IP joint, indicating varus instability (Figure 1).
• Intraoperative assessment:
  • The middle portion of the collateral ligament had healed with scar tissue that was insufficient for direct repair or plication.

Surgical Technique: Lateral Collateral Ligament Reconstruction

• Indication: chronic varus instability of the hallux IP joint with failed conservative management.
• Donor tendon: Palmaris longus tendon harvested from the forearm (minimally invasive harvest via two small transverse incisions).
• Approach: Lateral longitudinal incision over the IP joint; joint exposure dorsal to the volar neurovascular structures.
• Preparation:
  • Drill holes created parallel to the joint at the normal insertion sites of the collateral ligament.
  • The damaged/deficient collateral ligament tissue was insufficient for repair; a tendon graft was required.
• Graft passage:
  • The tendon graft was passed through the drilled holes from the lateral wound to the medial side.
  • The two ends of the graft were tied on the medial side after confirming full ROM (Figures 2 and 3).
• Postoperative immobilisation and rehabilitation:
  • Immobilisation for 4 weeks.
  • After immobilisation, active range of motion (ROM) exercises were started.
  • At 3 months, the patient was allowed to participate in training activities.
• Outcomes:
  • At 12 months: the IP joint remained stable and congruent with no varus instability; flexion was $45^ ext{°}$, extension full, compared with the uninjured toe having $60^ ext{°}$ of flexion (Figure 5).
  • Figures 2–5 document intraoperative and postoperative status (consent obtained for publication).

Postoperative Course and Rehabilitation Details

• Immediate post-op: immobilisation for $4 ext{ weeks}$.
• Early rehabilitation: initiation of active ROM exercises after immobilisation period.
• Intermediate phase: gradual progression to functional activity; by $3 ext{ months}$, patient could train.
• Long-term follow-up: at $12 ext{ months}$, joint was stable and congruent with preserved motion (39–? degrees range; note: flexion $45^ op\circ$) on the operated side and full extension.

Outcomes and Follow-Up

• Symptom resolution: asymptomatic at 12 months.
• Stability: hallux IP joint remained stable with no varus translation.
• ROM:
  • Operated toe: $45^ ext{°}$ of flexion; full extension.
  • Contralateral/uninjured toe: $60^ ext{°}$ of flexion, indicating some loss of flexion on the operated side but still functional for kicking and training.
• Overall assessment: successful reconstruction with preserved joint mobility suitable for taekwondo training.

Comparison with Existing Knowledge and Study Contributions

• What is already known:
  • The hallux IP joint is inherently stable in the transverse plane compared with the MTP joint.
  • Taekwondo has a high risk of lower-extremity injuries due to rapid, powerful kicking actions.
• What this study adds:
  • Reports a rare case of varus instability of the hallux IP joint in a taekwondo athlete.
  • Demonstrates that lateral collateral ligament reconstruction with a palmaris longus tendon graft can provide a stable and mobile IP joint, enabling continued training.
• Practical implications:
  • Taekwondo athletes should be warned about this potential forefoot injury.
  • Lateral collateral ligament reconstruction can be an effective treatment for chronic varus instability of the hallux IP joint.

Implications for Taekwondo Training, Equipment, and Prevention

• Taekwondo technique emphasizes fast, powerful kicks using the dorsum or lateral aspect of the foot, increasing risk for forefoot injuries, including IP joint instability.
• Protective equipment in Olympic-style taekwondo now includes headgear, chest protectors, shin pads, and padding for hands and feet; however, current foot protectors may not cover the interphalangeal joint, leaving it vulnerable to high-speed impacts.
• Recommendations:
  • Athletes should be warned about potential IP joint injuries.
  • Consider protective enhancements that cover the IP joint area.
  • During training and competition, mats and surface conditions should be checked to minimize hyperextension or stubbing injuries.

References and Contextual Notes

• The report cites injuries and mechanisms around the MTP joint and other hallux injuries, with several references (e.g., prospective discussions of plantar plates, sesamoid pathology, dislocations, and martial arts injuries) to establish context for the rarity and management of hallux IP joint instability.
• Notable references mentioned include work on injuries around the hallux IP joint, dorsal dislocations, and martial arts injury comparisons, as well as taekwondo injury statistics and Olympic trials data for injury rates.
• Publication details:
  • Case report published in Br J Sports Med 2007;41:917–919; doi: 10.1136/bjsm.2007.035501.
• Ethical considerations:
  • Informed consent was obtained for publication of the figures (Figures 1–5).

Additional Observations and Considerations

• Alternative options discussed: arthrodesis could provide more definite stability but would reduce interphalangeal mobility critical for push-off in athletic activities.
• Rationale for graft choice: palmaris longus tendon was selected due to presumed minimal donor-site morbidity and routine use in ligament reconstructions; the author notes that most taekwondo techniques rely on lower extremity function, so preserving ankle-driven mobility and foot function is essential.
• Rehabilitation goals: restore function sufficiently to allow participation in training without pain or instability; balance between stability and mobility to optimize performance in kicks and foot placement.

Key Numerical References (for quick review)

• Age: $19$ years old.
• Flexion on operated toe at 12 months: $45^ ext{°}$ vs contralateral toe: $60^ ext{°}$.
• Immobilisation duration: $4 ext{ weeks}$.
• Time to resume training: $3 ext{ months}$ postoperatively.
• Follow-up: $12 ext{ months}$.

Figures (as described in the article)

• Figure 1: Stress radiograph showing marked widening of the lateral side of the left IP joint.
• Figure 2: Palmaris longus tendon graft passing through the holes at collateral ligament insertion sites.
• Figure 3: Tendon graft limbs tied on the medial side.
• Figure 4: One year post-op image showing a congruent IP joint.
• Figure 5: Degree of flexion of the operated IP joint (44–46 degrees) compared to the normal side.
• Images were obtained with informed consent for publication.

Wordings to Remember for Exam Context

• The hallux IP joint relies on a combination of collateral ligaments, plantar plate, joint capsule, and tendinous structures for stability in multiple planes; injury patterns may favor fractures over purely ligamentous injuries due to the joint’s inherent stability.
• In athletes, particularly taekwondo practitioners, preserving mobility can be as important as achieving stability; thus, ligament reconstruction with autograft tendons can be preferred over fusion when a mobile, functional IP joint is desirable.
• Protective equipment and training environments should address the vulnerability of small joints like the hallux IP joint, especially given the sport's emphasis on kicks and ground contact.

Summary Takeaways

• Varus instability of the hallux IP joint is rare but can occur in high-demand athletes such as taekwondo practitioners.
• Surgical reconstruction using the palmaris longus tendon can restore stability and maintain enough motion for athletic performance.
• Careful imaging, including varus stress views, helps confirm instability when standard radiographs are unrevealing.
• Rehabilitation and timing are critical to achieving a functional return to sport while minimizing instability.