Biomechanics of Hallux Abducto Valgus PDF

THE BIOMECHANICS OF HALLUX ABDUCTO VALGUS JARROD SMITH, DPM, FACFAS ASSISTANT PROFESSOR LEARNING OBJECTIVES Identify anatomical structures which govern the function of the first metatarsophalangeal joint Recognize the role of excessive pronation in the development of hallux abducto valgus Describe t...

THE BIOMECHANICS OF HALLUX ABDUCTO VALGUS JARROD SMITH, DPM, FACFAS ASSISTANT PROFESSOR LEARNING OBJECTIVES Identify anatomical structures which govern the function of the first metatarsophalangeal joint Recognize the role of excessive pronation in the development of hallux abducto valgus Describe the stages of hallux abducto valgus development with their radiographic findings INTRODUCTION TO HALLUX ABDUCTO VALGUS DEFORMITIES Hallux abducto valgus (HAV) and bunion are synonymous Bunion – derived from the French word buigne meaning “bump on the head.” A localized swelling at either the medial or dorsal aspect of the first metatarsophalangeal joint HALLUX-ABDUCTO-VALGUS (HAV) Hallux Abductus – deviation to a lateral position (from the body midline) Transverse plane deformity Hallux Valgus – part assumes the position of eversion Frontal plane deformity PHYSICAL EXAMINATION Transverse plane mobility Normally little to no motion without an HAV deformity HAV- mobility can increase PHYSICAL EXAMINATION Sagittal plane motion of the first ray Normal is 10 mm total (5 mm dorsiflexion & 5 mm plantarflexion) Hypermobility = > 15 mm total excursion (often associated with generalized ligamentous laxity) Another sign of probable 1st ray hypermobility is sub 2nd metatarsal head pain PHYSICAL EXAMINATION Sagittal plane motion of the MTPJ Quality of 1st MTPJ motion is evaluated with a retrograde force across the joint as it is taken through full ROM in the deviated position and corrected position. The retrograde force causes contact of the proximal and distal cartilage PHYSICAL EXAMINATION Crepitus = Articular damage Poor quality of motion = structural adaptation of cartilage PHYSICAL EXAMINATION Axis of motion of the 1st MTPJ Dorsiflexion and plantarflexion in the corrected position Tendency to deviate into abnormal position = tracking (B,C,D) Inability to adduct the hallux (E) = track-bound Tracking is largely dependent on lateral soft tissue contracture Lateral capsule Adductor hallucis PHYSICAL EXAMINATION Hallux interphalangeal joint Evaluate for sagittal and transverse plane deformity PHYSICAL EXAMINATION Pain location The entirety of the 1st MTPJ should be palpated for symptoms Structures of the foot are always in close proximity making physical evaluation more challenging Need to be deliberate and systematic in your examination PHYSICAL EXAMINATION Presence of hyperkeratotic lesions Calluses tell the story of how the foot is functioning Pinch callus = abnormal pronatory roll off Sub met 1 = Plantarflexed first ray/hypertrophic sesamoid Sub 2nd met = 1st ray insufficiency/metatarsus primus elevatus/2nd toe pathology PHYSICAL EXAMINATION Hallux position No contact Abutting Overlying Underlying FIRST RAY ANATOMY AND BIOMECHANICS There are NO tendinous attachments to the first metatarsal head. No tendon to assist with stability FIRST RAY ANATOMY AND BIOMECHANICS First ray stability is dependent on: Congruent and stable 1st MTPJ during push off A proximal articular set angle (PASA) that encourages stability Balanced static and dynamic constraints Stable first tarsometatarsal joint PATHOLOGIC FACTORS OF HALLUX ABDUCTO VALGUS EXTRINSIC FACTORS INTRINSIC FACTORS Footwear Sexual dimorphism High-heeled shoes Narrow toe boxed shoes Excessive weightbearing Excessive load Age Genetics Joint morphology Metatarsal parabola Ligamentous laxity Pes planus First ray hypermobility Equinus EXTRINSIC FACTORS Focal point of your patients Patient’s often blame their shoe choices for their bunion deformities They wonder about their weight and its impact on their feet Does it really matter??? EXTRINSIC FACTORS Footwear Does not explain the prevalence of hallux valgus in the populations of people who do not wear shoes Does not explain many individuals who wear high-heeled, narrow toed shoes and do not develop HAV or any foot symptoms Shoe gear does not appear to affect juvenile HAV Shoes play a role in enabling progression of HAV May speed up HAV development, but do not cause it. EXTRINSIC FACTORS Excessive weightbearing No proven link between excessive walking and bunion formation Excessive load Elevated body mass index (BMI) No proven link between obesity and bunion formation Ballet dancing is the exception There is a strong correlation between ballet dancing and forefoot pathology INTRINSIC FACTORS Sexual dimorphism Age Genetics Joint morphology Metatarsus parabola Ligamentous laxity Pes planus First ray hypermobility Equinus INTRINSIC FACTORS Sexual dimorphism Overall, the correlation of gender to bunion formation is unknown 1:15 ratio male to female for elective surgical bunion correction Females tend to have a more rounded 1st metatarsal head Females tend to be more hypermobile than males Females tend to have a more adducted 1st metatarsal due to a more oblique medial cuneiform Ligamentous laxity increases prior to child-birth due to relaxin and progesterone INTRINSIC FACTORS Age Biomechanical changes occur with age Muscle strength Gait Peak onset of bunion formation is between 30 and 60 year of age Too many variables within age to say it has a direct correlation INTRINSIC FACTORS Genetics Play a major role in foot pathology Joint morphology First metatarsal head shape Medial cuneiform shape Anatomic variances Ligamentous make-up Foot-type Range of motion GENETIC FACTORS Joint morphology First metatarsal head shape A. Round – most unstable B. Square – stable C. Square with ridge – most stable *Arthritic conditions can alter head shape GENETIC FACTORS Joint morphology Medial Cuneiform Obliquity Oblique = unstable “Atavistic” cuneiform Atavism is a modification of a biological structure whereby an ancestral genetic trait reappears after having been lost through evolutionary change in previous generations. GENETIC FACTORS Joint morphology Medial Cuneiform Obliquity Oblique = unstable “Atavistic” cuneiform Atavism is a modification of a biological structure whereby an ancestral genetic trait reappears after having been lost through evolutionary change in previous generations. GENETIC FACTORS Metatarsal parabola Has a profound affect on how the foot functions This has implications as to how a bunion forms, but also how the foot functions after bunion surgery Studies have shown an increased correlation of HAV with a “Morton Foot” (short 1st metatarsal) GENETIC FACTORS Ligamentous laxity Plays a large role in bunion formation of both adults and juveniles 70% of juveniles with bunions also show clinical hypermobility Wynne-Davies testing to evaluate for hypermobility GENETIC FACTORS Pes planus à pronation Destabilizes the medial column Produces an elevation of the first metatarsal Causes the peroneus longus to lose its function Increases loading on the plantar medial border of the hallux at heel rise Mechanical pull is lost Locking mechanism is lost GENETIC FACTORS First ray hypermobility Functional metatarsus primus elevatus GENETIC FACTORS Equinus Tight gastrocnemius à gastrocnemius equinus Tight triceps surae à gastrosoleal equinus Early and increased forefoot overload Pronation Loss of medial column stability Metatarsus primus elevatus Increased potential for progression of HAV WHAT DOES THIS MEAN AND WHAT DOES IT LEAD TO? Everything in foot function is related to foot pathology Rarely is there a scenario where “one thing” results in a foot deformity Multiple intrinsic factors will lead to a sequential failure of structures leading to the progression of hallux abducto valgus Ten steps of bunion formation STEP 1 Failure of the medial supporting structures of the metatarsophalangeal joint Medial sesamoid ligament Medial collateral ligament Ligaments become elongated from increased stretching pressure Failure is early and essential STEP 2 The metatarsal head begins to drift medially The metatarsal head “slips off” the sesamoidal apparatus STEP 3 The proximal phalanx moves into an abducto valgus position STEP 4 The metatarsal head sits on the tibial sesamoid Leads to erosion of cartilage and the median crista The fibular sesamoid appears within the intermetatarsal space STEP 4 The metatarsal head sits on the tibial sesamoid Leads to erosion of cartilage and the median crista The fibular sesamoid appears within the intermetatarsal space STEP 5 The bursa overlying the medial eminence can thicken This can increase pressure effects of shoe gear on the medial eminence STEP 6 The extensor hallucis longus and the flexor hallucis longus bowstring laterally This increases the valgus displacement of the hallux STEP 7 The metatarsal head drops off the sesamoidal apparatus due to frontal plane rotation STEP 8 The abductor hallucis becomes dysfunctional The plantomedial insertion of the abductor hallucis rotates inferiorly The balance between the abductor hallucis and the adductor hallucis is lost STEP 9 The weaker, dorsal capsule rotates medially as it loses tendinous reinforcement causing further joint instability STEP 10 The metatarsal head elevates and transfers plantar pressures laterally Results in lesser MTPJ overload à metatarsalgia STAGING OF HALLUX ABDUCTO VALGUS First MTPJ alignment A. Congruous joint lines are parallel lines intersect outside the joint space B. Deviated joint C. Subluxed joint lines intersect inside the joint space STAGES OF HALLUX ABDUCTO VALGUS Stage 1 Clinical biomechanical dysfunction of the 1st MTPJ Radiographic angles are all normal Radiographically normal with a congruous 1st MTPJ STAGES OF HALLUX ABDUCTO VALGUS Stage 2 Alignment of the 1st MTPJ is deviated The hallux is abducted (hallux abductus angle is abnormal) The first metatarsal alignment is WNL (intermetatarsal angle is normal) STAGES OF HALLUX ABDUCTO VALGUS Stage 3 Alignment of the 1st MTPJ is deviated The hallux is abducted (hallux abductus angle is abnormal) The first metatarsal alignment is abnormal (intermetatarsal angle is abnormal) STAGES OF HALLUX ABDUCTO VALGUS Stage 4 Alignment of the 1st MTPJ is subluxed The hallux is abducted (hallux abductus angle is abnormal) The first metatarsal alignment is abnormal (intermetatarsal angle is abnormal) STAGES OF HALLUX ABDUCTO VALGUS REFERENCES Gerbert J. Textbook of Bunion Surgery. 3rd ed. Philadelphia: W.B. Saunders; 2001. https://www.sciencedirect.com/book/9780721677842/textbook-of-bunionsurgery Coughlin MJ. Mann RA. Saltzman CL. Surgery of the Foot and Ankle. 8th ed. St. Louis: Mosby; 2007. QUESTIONS COPYRIGHT NOTICE This presentation may contain copyrighted material used for educational purposes under the guidelines of Fair Use and the TEACH Act. It is intended only for use by students enrolled in this course. Reproduction or distribution is prohibited. Unauthorized use is a violation of the DMU Integrity Code and may also violate federal copyright protection laws.