Applied animal biomechanics
4.7 Equine peripheral joints
Due to the interest in equine locomotion, there is a significantly larger bank of biomechanics research regard-ing the equine peripheral joints than for those of the canine;
both relating to kinematics and forces about the joints
during gait. Table 4.2 summarises the equine peripheral joints, but there are notes in the text, particularly regarding joint forces during gait. Two very comprehensive texts summarising a large portion of the current literature related to equine locomotion and biomechanics are; Back &
Clayton (2001) Equine Locomotion, and Hodgson & Rose
Table 4.2 A summary of the equine peripheral joints: joint type, articular surfaces, the primary motion of the joint and the accessory movements that occur at each complex. Adapted from Budras et al.(2002)
Joint Glenohumeral
Elbow
Carpus
Metacarpophalangeal joint (Fetlock)
Proximal interphalangeal joint (Pastern)
Distal interphalangeal joint (Coffin joint)
Coxofemoral joint (Hip)
Stifle
Tarsal joint (Hock)
Metatarsophalangeal joint Proximal and distal interphalangeal joints Temporomandibular
Joint type and articular surfaces
Spheroid,between the glenoid cavity of the scapula and the head of humerus, with the glenoid fossa on the scapula deepened by the glenoid labrum
Composite joint formed by the humeral condyle and the head of the radius (humeroradial joint) and the semilunar notch of the ulna (humeroulnar joint) – both simple hinge joints. Proximal radioulnar joint communicates with the main elbow joint – a simple pivot joint
Composite joint made up of radiocarpal joint involving trochlea of radius and carpals (condylar); midcarpal joint involving proximal and distal carpal rows (condylar);
carpometacarpal joint involving carpal bones II–IV and metacarpals II–IV (plane) and intercarpal joints involving carpals of the same row (plane)
Compound articulation between third metacarpal, proximal phalanx and proximal sesamoid bones – composite hinge joint
Simple saddle joint between proximal and middle phalanx.
(Forelimb and hindlimb)
Composite saddle joint between middle phalanx, distal phalanx, with hoof cartilage and navicular bone (Forelimb and hindlimb)
Composite spheroid joint, articulation between the femoral head and the acetabulum of the ilium, ischium and pubis. The acetabulum is deepened by a band of fibrocartilage on the rim of the acetabulum
Complex joint, comprising the tibiofemoral joint (simple condylar) and the patellofemoral joint (simple, gliding joint). At the tibiofemoral joint, the convex femoral condyles articulate with the tibial condyles. The patellofemoral joint is between the patella and the trochlea of the femur
The hock complex includes the tarsocrural joint (simple cochlear joint) proximal and distal intertarsal joints, tarsometatarsal joint (composite plane joints) and intertarsal joints (perpendicular tight joints). The greatest amount of movement occurs at the tarsocrural joint
See forelimb See forelimb
Is a simple condylar joint which allows translatory movement, with an articular disc
Main movement Flexion and extension
Flexion–extension. No movement at proximal radioulnar joint
Flexion–extension at radiocarpal (up to 90°);
flexion–extension at midcarpal (up to 45°); carpometacarpal joint little planar motion;
intercarpal joint little planar movements
Flexion and extension
Flexion and extension
Flexion and extension
Flexion and extension are the main movements
The main movements at the stifle are flexion–extension at the tibiofemoral joint, with the patella gliding in the trochlea during the movement
At the tarsocrural joint, flexion–extension. The intertarsal, proximal and distal tarsal (tarsometatarsal) joints undergo small amounts of translatory and rotatory movements during locomotion
Hinge – opening and closing
Accessory movement Rotation and minimal ab/adduciton
Minimal
Slight accessory rotation and lateral glide at radiocarpal joint
During flexion, small amounts of ab/adduction and axial rotation
Axial rotation and lateral movements
Axial rotation and lateral movements
Multidirectional minimal abduction/adduction
Tibiofemoral joint – at extreme extension there is accessory external rotation, and with flexion, accessory internal rotation
At the tarsocrural joint, lateral and rotatory accessory movements
Lateromedial excursion; rostral glide of mandible with opening
Carpus
There are three joints of the carpus:
•
antebrachiocarpal(radiocarpal) joint (between the distal radius and ulna and proximal carpal row);•
intercarpal joint (between proximal and distal carpal rows); and•
carpometacarpal joint (between distal carpal row and proximal ends of metacarpals).The proximal and middle joints are ginglymi, but the distal joint is planar. The joints formed between the adjacent carpal bones of each row are also planar (Getty 1975). Main movement of the carpus as a whole is flexion–extension.
With flexion there is slight accessory rotation and lateral glide available. These movements occur mostly at the radio-carpal joint and interradio-carpal joints.
Just after initial ground contact during walking gait, the carpus rapidly assumes its close packed position between 7 and 12% of stride, to allow the limb to act like a propulsive strut through stance phase (Hodsonet al. 2000; Clayton et al. 2001). The carpus then does not flex until breakover, with peak flexion occurring at 76% of stride. The carpus does not play an important role in energy absorption or generation during walking gait, but plays an active role in initiating breakover (Claytonet al. 2000).
Metacarpophalangeal joint
The fetlock, or metacarpophalangeal joint, is a ginglymus formed between the distal third metacarpal and the prox-imal end of the proxprox-imal phalanx. In stance the joint is an extension angle of 140° (approximately 150° in the hind fetlock). The main movements at the fetlock are flexion–
extension. During flexion, accessory movements of abduc-tion, adduction and rotation can occur (Getty 1975).
The fetlock extends through early stance phase of walk.
Maximal extension occurs at around 34% of stride, when forces during gait change from braking to propulsive (Hodsonet al.2000). After this point the fetlock flexes for the remainder of stance phase. It continues to flex during breakover, with peak flexion occurring at 82% of stride, during swing. The fetlock has been described as functioning elastically, as there is an initial absorption of energy during early stance and bursts of energy generation in late stance and during breakover. It shows bursts of energy absorption also during swing phase, at 86% of stride (Claytonet al. 2000).
Pastern joint and coffin joint (Fore)
The pastern joint is the articulation of the proximal and middle phalanges and is classified as a ginglymus (Getty 1975). The joint is extended in stance. The main movement at the pastern joint is flexion–extension, which moves through 35° during the stance phase (Claytonet al. 2000).
Accessory movements of medial and lateral flexion are available when the joint is flexed (Getty 1975).
(1994)The Athletic Horse: Principles and practice of equine sports medicine. These books may be a useful adjunct for those physiotherapists working with horses.
Scapulothoracic joint
The horse has no clavicle, so the thoracic limb is attached to the trunk via muscles – a synsarcosis(Budraset al. 2001), and also the dorsal scapular ligament. The movement of the shoulder on the thorax is rotation around a transverse axis passing through the scapula caudal to the dorsal part of the scapular spine (Getty 1975).
Glenohumeral joint
The glenohumeral articulation is formed between the distal end of the scapula (glenoid cavity) and the head of the humerus (Getty 1975). The main movement at the shoulder joint is flexion and extension. In stance, the angle between scapula and humerus is approximately 120°. There are some accessory rotatory movements, which have been noted when the stabilising muscles are removed. When the horse is not weight bearing on the limb, rotation can be achieved manually, however no motion measurements have been found in the literature (Getty 1975). This may implicate soft tissues such as the lacertus fibrosus, which may have a similar role to the dynamic stabilising muscles in the human.
The shoulder joint extends during most of swing phase of walk, to ground contact and early stance phase (Hodson et al. 2000). During early stance phase the shoulder flexes and then tends to maintain a constant angle during periods of bipedal support, and flexes slightly during tripedal sup-port phase. At breakover the shoulder flexes further. The shoulder has been described as acting as an energy damper during stance phase of the walk, and also shows absorption of power during swing phase (Claytonet al. 2000).
Elbow
The elbow is a ginglymus between the distal trochlear sur-face of the humerus and the fovea of the proximal radius plus trochlear notch of the ulna (Getty 1975). The move-ments available are flexion and extension. In stance, the articular angle is 150°. There is little appreciable movement at the radioulnar joint, with the forearm being fixed in pronation (Getty 1975).
The elbow remains at a constant angle throughout the first 7% of walking stride, then, during breakover, which occurs between heel off (55% of stride) and lift off (64% of stride) it moves into flexion. The elbow shows a single flexion cycle during swing that elevates the distal limb ing that phase. It reaches peak flexion at 84% of stride dur-ing swdur-ing phase (Hodsonet al. 2000). The elbow shows net generation of energy to maintain the limb in extension dur-ing early stance phase and is the main joint of energy gener-ation during walk gait in the forelimb (Claytonet al. 2000).
The coffin joint is the articulation between the middle and distal phalanges and is in contact on the palmar aspect with the navicular (distal sesamoid) bone (Getty 1975). In stance the joint is extended, and the main movements at the joint are flexion–extension. Accessory movements of lateral and medial flexion and rotation are available when the joint is in relative flexion (Getty 1975). Flexion–extension pat-terns in the pastern joint appear to mirror that of the coffin joint (Claytonet al. 2000). The pastern joint flexes for up to 10% of the stride (early stance) then reverses direction after this point. Flexion then occurs again during breakover and shows peak flexion during swing, at 84% of total stride (Hodsonet al. 2000). The coffin joint has been described as an energy damper during stance, with a small amount of energy generation at the beginning of breakover (Clayton et al. 2000).
Coxofemoral (Hip) joint
The coxofemoral joint is the articulation formed by the head of the femur and the deep ilial acetabulum bounded by a rim of fibrocartilage. Two ligaments, the ligament of the femoral head and the accessory ligament limit internal rotation and abduction of the hip joint. Thus the main movements are primarily flexion and extension, which are responsible for protraction and retraction of the entire hind limb during walking gait (Hodsonet al. 2001). Maximal protraction occurs just before the end of swing phase and maximal retraction occurs at breakover. The hip joint is the main source of energy generation during stride, at the walk (Clayton 2001a).
Tibiofemoral and patellofemoral articulation (Stifle) The stifle is made up of the tibiofemoral and patellofe-moral joints. The congruence of this tibiofepatellofe-moral joint is enhanced by the menisci. The patella glides proximally and distally on the trochlea during tibiofemoral extension and flexion, respectively (Getty 1975).
In the standing position the articular angle is 150° (Getty 1975). The main movements at the tibiofemoral joint are flexion and extension, with the accessory translation of the tibia in a craniocaudal direction restricted by the cruciate ligaments (Clayton 2001a). At extreme extension there is accessory external rotation, and with flexion, accessory internal rotation (Getty 1975).
At walk, during the initial 10% of stride, which is a period of rapid loading, the stifle joint flexes (Hodsonet al. 2001).
The stifle begins to flex further when the hind limb is retracted beyond the midstance position, and flexion of stifle occurs with the swing phase and protraction of the limb, with the hock, which raises the distal limb. The stifle begins to extend in preparation for ground contact at about 80% of total stride.
The stifle joint absorbs equal amounts of energy in the stance and the swing phase of walk (Clayton 2001a).
Tarsocrural and tarsometatarsal joint (Hock)
The hock is a composition of articulations, with most of the movement occurring at the most proximal joint, the tarsocrural joint, which is classified as a ginglymus (Getty 1975). In the standing position the angle of the hock is approximately 150° (Getty 1975). The distal tibia rotates around the trochlea of the talus, allowing the main move-ment of flexion–extension to occur, along with lateral and rotatory accessory movements. These articular surfaces are directed obliquely dorsal and laterally at an angle of 12–15° (Getty 1975).
The intertarsal and distal tarsal (tarsometatarsal) joints undergo small amounts of translatory and rotatory move-ments during locomotion. Clayton (2001b) presents some kinematic data on the movement at the distal tarsal joints, as this is most often the site of bone spavin. During the stance phase of walk, the cannon bone internally rotates at the distal joints and then slides cranially. This cranial slide becomes ‘de-coupled’ in swing by the time the hock is flexed to 50°, and re-couples later in swing as the joint reaches the same angle. During swing phase, at about 80%
of stride, the hock reaches peak flexion along with the stifle (Hodsonet al. 2001). After this, the hock extends in preparation for ground contact.
The hock joint assists the hips in generation of energy of stride during both stance and swing phases of walk (Clayton 2001b).
Metatarsophalangeal joint (Hind)
During the initial 10% of walking stride, a period of rapid loading, the fetlock joint extends (Hodsonet al. 2001).
Pastern joint/coffin joint (Hind)
At 5% of stride (early stance phase) the coffin joint shows a peak in flexion. The coffin joint shows a peak in flexion at 80% of stride during swing phase. After this point it extends in preparation for ground contact (Hodsonet al. 2001).
The biomechanics of the fetlock, pastern and coffin joints in the hindlimb have been likened to those of the forelimb (Getty 1975).
Temporomandibular joint
The temporomandibular joint (TMJ) is a complex diarthrodial joint formed between the articular tubercles of the temporal bone and the condylar processes of the mandible. A fibrocartilagenous disc improves the congru-ency between the articular surfaces, and divides the joint into a dorsal and a ventral compartment (Maierlet al. 2000;
Moll & May 2002; Baker 2002). The mandibular condyles are at an angle of 15° in a plane that runs laterocaudal to ventromedial and a plane that runs mediocaudal to laterorostral. TMJ movements are around a transverse axis.
When the mouth opens, the mandibular condyle moves slightly in a rostral direction (Baker 2002).
data are presented in a force–time curve, or numerically (McLaughlin 2001). Vertical force is usually the largest of the orthogonal forces, with mediolateral and craniocaudal braking forces generally smaller. Force data are also nor-malised with respect to the dog’s body weight, (McLaughlin 2001) which means dogs of different breeds can be compared.
Walking data
Walking in the quadruped involves a cyclic exchange of gravitational potential energy and kinetic energy of the centre of mass. In a study by Griffinet al. (2004) kinematic and ground reaction force data were collected from dogs walking over a range of speeds. The authors found that the forequarters and hindquarters of dogs behaved like two independent bipeds, with the centre of mass moving up and down twice per stride. Up to 70% of the mechanical energy required to lift and accelerate the centre of mass was recov-ered via a mechanism likened to an inverted pendulum (Griffinet al. 2004). Using a model of two inverted pendu-lums, these authors concluded that there are two reasons why dogs did not walk with a flat trajectory of the centre of mass:
1. Each forelimb lagged its ipsilateral hindlimb by only 15% of the stride time – this produced time periods when the forequarters and hindquarters moved up or down simultaneously.
2. Forelimbs supported 63% of body mass during gait.
(This is consistent with during static four-legged weight bearing.)
The model proposed here predicts that the centre of mass of a dog will undergo two fluctuations per stride cycle.
In an attempt to establish some normative data in large-breed dogs, Hottingeret al. (1996) have presented data on the stance and swing phase of gait at the walk, pertaining to the joint angles, total time of stance and swing phase of each limb. It is beyond the scope of this chapter to reproduce the author’s data, but the reader is directed to this research as a useful resource.
Lameness data
A population of adult Labrador Retrievers – 17 subjects free of orthopaedic and neurologic abnormalities, 100 with uni-lateral cranial cruciate ligament (CCL) rupture, and 131 studied 6 months after surgery for unilateral CCL injury, 15 with observable lameness – were walked over a force platform, with ground reaction force (GRF) recorded during the stance phase (Evanset al. 2005). The probability of visual observation detecting a gait abnormality was compared with that of force platform gait analysis. During the stance phase, it was determined that a combination of peak vert-ical force (PVF) and falling slope were optimal for discrim-inating sound and lame Labradors. After surgery, 75% of subjects with no observable lameness failed to achieve GRFs 4.7.1 Summary
Compared with the vertebral column there has been little kinematic research carried out in the peripheral joints, particularly in the canine. In the equine there has been some data developed regarding forces and torques acting about the peripheral joints. As with the vertebral column, physiotherapists can only be guided by the current know-ledge of anatomy and morphology and the growing field of kinematics and motion analysis in the canine and equine peripheral joints.