title: Biomechanical evaluation of the craniovertebral junction after unilateral joint-sparing condylectomy: implications for the far lateral approach revisited.
abstract: OBJECTIVE The far lateral transcondylar approach to the ventral foramen magnum requires partial resection of the occipital condyle. Early biomechanical studies suggest that occipitocervical (OC) fusion should be considered if 50% of the condyle is resected. In clinical practice, however, a joint-sparing condylectomy has often been employed without the need for OC fusion. The biomechanics of the joint-sparing technique have not been reported. Authors of the present study hypothesized that the clinically relevant joint-sparing condylectomy would result in added stability of the craniovertebral junction as compared with earlier reports. METHODS Multidirectional in vitro flexibility tests were performed using a robotic spine-testing system on 7 fresh cadaveric spines to assess the effect of sequential unilateral joint-sparing condylectomy (25%, 50%, 75%, 100%) in comparison with the intact state by using cardinal direction and coupled moments combined with a simulated head weight "follower load." RESULTS The percent change in range of motion following sequential condylectomy as compared with the intact state was 5.2%, 8.1%, 12.0%, and 27.5% in flexion-extension (FE); 8.4%, 14.7%, 39.1%, and 80.2% in lateral bending (LB); and 24.4%, 31.5%, 49.9%, and 141.1% in axial rotation (AR). Only values at 100% condylectomy were statistically significant (p < 0.05). With coupled motions, however, -3.9%, 6.6%, 35.8%, and 142.4% increases in AR+F and 27.3%, 32.7%, 77.5%, and 175.5% increases in AR+E were found. Values for 75% and 100% condyle resection were statistically significant in AR+E. CONCLUSIONS When tested in the traditional cardinal directions, a 50% joint-sparing condylectomy did not significantly increase motion. However, removing 75% of the condyle may necessitate fusion, as a statistically significant increase in motion was found when E was coupled with AR. Clinical correlation is ultimately needed to determine the need for OC fusion.
authors.affiliation: Department of Neurological Surgery, Cleveland Clinic.|Spine Research Lab, Lutheran Hospital, Cleveland Clinic Center for Spine Health; and.
authors.forename: Varun R
authors.initials: VR
authors.lastname: Kshettry
authors.affiliation: Department of Neurological Surgery, Cleveland Clinic.|Spine Research Lab, Lutheran Hospital, Cleveland Clinic Center for Spine Health; and.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Healy
authors.affiliation: Spine Research Lab, Lutheran Hospital, Cleveland Clinic Center for Spine Health; and.
authors.forename: Robb
authors.initials: R
authors.lastname: Colbrunn
authors.affiliation: Spine Research Lab, Lutheran Hospital, Cleveland Clinic Center for Spine Health; and.
authors.forename: Dylan T
authors.initials: DT
authors.lastname: Beckler
authors.affiliation: Department of Neurological Surgery, Cleveland Clinic.|Spine Research Lab, Lutheran Hospital, Cleveland Clinic Center for Spine Health; and.
authors.forename: Edward C
authors.initials: EC
authors.lastname: Benzel
authors.affiliation: Department of Neurological Surgery, Cleveland Clinic.|Section of Rhinology, Sinus and Skull Base Surgery, Head and Neck Institute, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Pablo F
authors.initials: PF
authors.lastname: Recinos
mesh_terms: D001269:Atlanto-Occipital Joint / Q000502:physiology*; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D009777:Occipital Bone / Q000601:surgery*; D059351:Organ Sparing Treatments; D010027:Osteotomy / Q000379:methods*; D011184:Postoperative Period; D016059:Range of Motion, Articular
keywords: AR = axial rotation; CVJ = craniovertebral junction; FE = flexion-extension; HWL = head weight load; LB = lateral bending; O = occiput; OC = occipitocervical; ROM = range of motion; SOC+C1 = suboccipital craniectomy with C-1 laminectomy; biomechanics; far lateral approach; occipital condylectomy; occipitocervical fusion; skull base surgery; spinal instability; spine