4:28

91. Cervical (PCM) Disc Replacement in Adjacent Segment

Diseased2 Year Follow-Up of 51 Cases

Paul McAfee, MD1, Luiz Pimenta, MD, PhD2, Matthew Scott-Young,

MBBS, FRACS3, Andrew Cappuccino, MD4; 1Spine and Scoliosis Center,

Towson, MD, USA; 2University of Sao Paulo, Brazil, Sao Paulo, Brazil;3Pacific Private Clinic, Southport, Queensland, Australia; 4Buffalo Spine

Surgery, Lockport, NY, USA

BACKGROUND CONTEXT: The theoretical advantage of cervical ar-

throplasty over cervical fusion is a reduced incidence of adjacent segment

disease.

PURPOSE: Adjacent segment disease with radiculopathy and neurologic

deficit adjacent to a nonmobile spinal segment is the ideal application for

cervical arthroplasty. Not only are the stresses and loads increased but un-

fortunately the previously fused segment is usually further compromised

by being fixed in a kyphotic position

STUDY DESIGN/SETTING: Prospective consecutive series of 51 pros-

thetic implantations placed adjacent to a previously fused ACDF cervical

segment. Patients presented with new onset of symptomatic radiculopathy

or myelopathy. This is the only prospective randomized cervical FDA IDE

which allows adjacent level fusions as part of the Inclusion Criteria.

PATIENT SAMPLE: Prospective consecutive series of 51 prosthetic im-

plantations with over 95% clinical and radiographic follow-up at 2 years

postoperatively–Class II Levels of Evidience.

OUTCOME MEASURES: Preoperative, 6 weeks, 3 months, 6 months,

1 year, and 2 year intervals – NDI, VAS, Odoms, TGIT, SF-36, and neu-

rological status. Radiographic outcomes included flex-ext and lateral bend-

ing ROM, disc space height, presence of HO, and translational stability.

METHODS: This is a prospective consecutive study of 51 PCM prosthe-

ses inserted in 41 patients with 60 adjacent segments previously fused or

rendered immobiled10 cases were performed as bilevel implantations.

The inclusion and exclusion criteria were otherwise identical to the normal

FDA prospective IDE criteria with all patients presenting with

radiculopathy and a corresponding neurologic deficit confirmed by an

MRI compressive lesion.

RESULTS: The mean preoperative cervical lordosis was 2.65 degrees

(�32 to 25), mean postoperative lordosis 12.3 degrees (-17 to 30), and

the mean improvement was 9.4 degrees of cervical lordosis (range �15

to 23). EBL50 to 100 cc with no patients requiring blood transfusions,

Length of surgery5mean 104 minutes (60 to 150) and the length of hos-

pital stay5mean 1.17 days (0 to 3 days). The clinical follow-up was

greater than 2 years. All patients were neurologically intact at follow-up

with a mean improvement of NDI550% and mean improvement in

VAS558.3%. The range of flexion and extension motion at the level of

the prosthesis was a mean of 8.9 degrees (range 4 to 20 degrees).

CONCLUSIONS: Naturally, the adjacent segment application of a cervical

disc replacement is a challenging clinical environment for cervical arthro-

plasty – by definition every case had prior surgery. Not only is the cervical

spine position often compromised by being in excessive kyphosis, but 19 of

the 60 previously fused levels had prior cervical instrumentation. Five pa-

tients had previous cervical cages, 2 had cage-plates, 7 patients had previous

anterior cervical plates, one had a prior arthroplasty device with HO, and 4

patients had PMMA which required revision. Despite the complicated na-

ture of the presenting pathology, the Porous Coated Motion Cervical pros-

thesis successfully restored some element of cervical lordosis, and restored

stability to the cervical segments. An added potential bonus is the preserved

8.9 degrees of flexion–extension mobility. The PCM appeared to work well

in these revision cases. This is the world’s largest study to date investigating

prospectively the value of cervical arthroplasty in adjacent segment disease.

FDA DEVICE/DRUG STATUS: Porous Coated Motion Cervical Disc

replacement: Investigational/not approved.

CONFLICT OF INTEREST: Author (PM) Consultant: Cervitech;

Author (PM) Grant/Research Support: Cervitech; Author (PM) Speaker’s

Bureau Member: Cervitech; Author (PM) Stockholder: Cervitech.

doi: 10.1016/j.spinee.2006.06.119

4:34

92. The Biomechanical Role of the Uncovertebral Joint in Cervical

Disc Arthroplasty: An In Vitro Cadaveric Model

Bryan Cunningham, MSc1, John C. Sefter, DO2, Nianbin Hu, MD1,

Helen Beatson, BA1, Paul McAfee, MD2, Juergen Harms, MD3; 1Union

Memorial Hospital, Baltimore, MD, USA; 2Spine and Scoliosis Center,

Towson, MD, USA; 3Spine Institute of Germany, Karlsbad, Germany

BACKGROUND CONTEXT: N/A

PURPOSE: This in vitro biomechanical study was undertaken to define

the multi-directional flexibility properties and biomechanical role of the

uncovertebral joints after cervical arthroplasty, and to determine their rel-

ative importance in stabilizing the operative motion segment after cervical

disc replacement.

STUDY DESIGN/SETTING: N/A

PATIENT SAMPLE: N/A

OUTCOME MEASURES: Biomechanical kinematic analysis

METHODS: Six fresh-frozen human cadaveric cervical spines were used

for the multi-directional flexibility testing and evaluated under the follow-

ing C5-C6 reconstruction conditions: 1) Intact, 2) Clinical discectomy, 3)

Radical discectomy to the lateral edge of the uncovertebral joint, 4) Porous

Coated Motion (PCM) Cervical Disc Replacement, 5) Unilateral uncover-

tebral resection (UNI), 6) UNIþPCM, 7) Bilateral uncovertebral resection

(BIL) with discectomy, and 8) BILþPCM. Unconstrained pure moments of

63.0 Nm were used for axial rotation, flexion-extension, and lateral bend-

ing testing, with quantification of the C5-C6 operative level range of

motion (ROM) and neutral zone (NZ).

RESULTS: Axial rotation loading for conditions of unilateral or bilateral

uncovertebral joint resection demonstrated significant increases in range of

motion compared with all other groups (p!.05). With insertion of the PCM

Cervical Disc, rotational stability of the unilateral resected uncovertebral

joint was restored to the intact segment for both range of motion and neu-

tral zone (pO.05). Bilateral uncovertebral resection combined with disc ar-

throplasty indicated significantly greater segmental motion that the intact

spine (p!.05). Flexion-extension testing demonstrated a significant in-

crease in range of motion for all groups with discectomy and uncovertebral

joint resection when compared with the intact condition or those stabilized

with the PCM arthroplasty (p!.05). PCM arthroplasty reconstruction after

discectomy restored the flexion-extension neutral zone and range of mo-

tion to the intact condition (pO.05). UNI and BIL uncovertebral joint re-

section demonstrated increased neutral zone values compared with all

other treatments (p!.05). Lateral bending indicated no difference in C5-

C6 range of motion for all treatment groups tested (pO.05). Neutral zone

values for the UNI and BIL uncovertebral joint resections were signifi-

cantly greater than all other treatments groups (p!.05); however, cervical

arthroplasty restored neutral zone levels to the intact condition (pO.05).

CONCLUSIONS: The current study highlights the biomechanical role of

the uncovertebral joint in cervical disc arthroplasty. Increased range of mo-

tion in all loading planesdaxial rotation, flexion–extension and lateral

bendingdwere observed following uncovertebral joint resection versus

discectomy alone. In contrast, discectomy alone resulted in increased seg-

mental flexion-extension motion, highlighting the biomechanical contribu-

tion of the bilateral uncovertebral joints in cervical spine stability. Cervical

arthroplasty after unilateral uncovertebrectomy restored segmental motion

to intact condition; however, segmental motion levels after bilateral resec-

tion remained statistically greater than intact condition. Maximal clinical

decompression for myelopathy may sometime include far lateral resection

of the uncovertebral joints. From a biomechanical standpoint, restoration

of segmental motion can be achieved with disc arthroplasty after unilateral

uncovertebrectomy; however, bilateral uncovertebral resection remains

a contraindication for cervical arthroplasty.

FDA DEVICE/DRUG STATUS: Porous Coated Motion Device: Investi-

gational/not approved.

CONFLICT OF INTEREST: Author (BC) Grant/Research Support: Cer-

viTech, Inc.

doi: 10.1016/j.spinee.2006.06.120

45SProceedings of the NASS 21st Annual Meeting / The Spine Journal 6 (2006) 1S–161S