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The snapping knee of infancy
Insights
Infants with joint laxity experienced painful knee snapping due to involuntary tibia subluxation, likely from biceps femoris muscle contractions. Symptoms resolved over time, suggesting symptomatic treatment is appropriate for this condition.
Area of Science:
- Orthopedics
- Pediatric Medicine
- Biomechanics
Background:
- Generalized joint laxity is a condition characterized by excessive flexibility in multiple joints.
- Family history is often considered in the diagnosis of musculoskeletal disorders.
- Knee pain and instability can affect individuals across various age groups.
Observation:
- Three infants with generalized joint laxity presented with painful, snapping episodes of the knee.
- These episodes were caused by involuntary, momentary lateral subluxation of the tibia.
- The subluxation appeared to be triggered by involuntary contractions of the biceps femoris muscle.
Findings:
- Involuntary lateral tibial subluxation in infants can manifest as painful knee snapping.
- The biceps femoris muscle's involuntary contraction is implicated in the mechanism of subluxation.
- Older children could voluntarily reproduce these subluxation events.
- Two affected children experienced a gradual cessation of involuntary subluxations over time.
Implications:
- This condition, potentially linked to neuromuscular control of the biceps femoris, warrants further investigation.
- Symptomatic management appears effective, as natural resolution was observed in followed cases.
- Understanding the biomechanics of tibial subluxation in lax joints can inform treatment strategies for pediatric knee conditions.
Abstract:
Three infants with generalized joint laxity and a negative family history had painful episodes of snapping of one or both knees caused by involuntary, momentary lateral subluxation of the tibia. These episodes of subluxation appeared to be due to involuntary contraction of the biceps femoris muscle. Older children learned to produce the phenomenon voluntarily. Treatment should be symptomatic, since the two children who were followed gradually stopped having involuntary subluxations.