In Vitro Mechanical Properties and Failure Mode of the Equine (Pony) Cranial Cruciate Ligament

Abstract

In vitro failure modes and mechanical properties of the equine cranial cruciate ligament (CCL) were evaluated in 15 stifle joints from 10 ponies. Ponies were from 3 to 25 years of age and weighed from 122 to 208 kg. Femur-CCL-tibia specimens were mounted in 48 degrees of flexion, distracted until a 500-g tensile preload was achieved, and then tested by tensile loading to failure. Specimens failed by complete midsubstance CCL rupture (n = 9), combined tibial insertion avulsion fracture and midsubstance CCL rupture (n = 4), and combined femoral origin avulsion fracture and midsubstance CCL rupture (n = 2). No significant differences were found between CCL mechanical properties and failure mode or body weight. Femur-CCL-tibia maximum tensile loads ranged from 1,945 to 4,326 N (median, 2,914 N). Mean maximum tensile load (N) per kilogram of body weight was 17.98 N/kg (median, 17.55 N/kg). These pony specimens had stiffer cranial cruciate ligaments (median, 320.2 N/mm) with a higher elastic modulus (median, 321.7 MPa) than has been reported for other species. Significant decreases in linear tensile load (P = .0292), maximum tensile load (P = .0493), and increases in strain to maximum load (P = .0463) were found in the specimens from 20- to 25-year-old ponies when compared with those from 3- to 10-year-old ponies.

Fracture of the medial intercondylar eminence of the tibia in horses treated by arthroscopic fragment removal (21 horses)

“…This study also confirms that MICET fractures are not avulsion fractures of the distal attachment of the CraCL as the CraCL was intact in 28.5% and only mildly damaged in 42.8% of the horses. This is further supported by an experimental study where the equine CraCL subjected to tension failed at mid‐substance in all specimens, avulsion fractures of the distal attachment of the CraCL without mid‐substance ligament rupture were not observed, and combined mid‐substance and fracture failure occurred in 4 of the 14 specimens tested .…”

“…Therefore, although MICET fractures are not avulsion fractures, damage to the CraCL may be present because of their anatomical proximity. In an experimental setting, combined mid‐substance CraCL failure and fracture of the MICET was suggested to occur more frequently in old animals . Although this injury combination was observed in some of the younger horses included in this study, further studies are necessary to further investigate this.…”

Fracture of the intercondylar eminence of the tibia treated by arthroscopic internal fixation

“…Fractures of the MICET are reported to be associated frequently with CRCL desmitis (Prades et al 1989;Butler et al 1993) although this has not always been this author's experience. When straining the CRCL to failure in pony cadavers, Rich and Glisson (1994) demonstrated avulsion fractures of the MICET in only 4/15 cases whereas 9/15 failed at mid-substance. Most of the attachment of the CRCL is cranial and lateral to the MICET (Sisson 1975).…”

“…Fractures of the intercondylar eminence of the tibia are thought to be caused by external trauma to the stifle joint or excessive pull on the cranial cruciate ligament (CRCL) (Sanders-Shamis et al 1988;Prades et al 1989;Dyson 1994;Rich and Glisson 1994). Successful conservative treatment has not been reported.…”

Avulsion of the cranial cruciate ligament insertion in a horse

“…With the increased use of arthroscopy in equine surgery, partial tearing of the cruciate ligaments and tibial eminence injuries without cruciate injury and meniscal injuries (Walmsley 1995) have been identified. Avulsion of the cruciate insertion on the femur is apparently quite rare as supported by an in vitro study (Rich and Glisson 1994). This paper describes the radiographic appearance of avulsion of the cranial cruciate ligament insertion in a horse, its attempted repair and the anatomical structures which prevented successful intervention.…”