Aspen Spinous Process Fixation System for Use in PLF in Patients With Spondylolisthesis

Evaluate the clinical outcomes of subject with spondylolisthesis undergoing posterolateral
fusion (PLF) surgery utilizing the Aspen™ Spinous Process Fixation System. The Aspen™ device
will be evaluated using Oswestry Disability Index (ODI) improvement and success of fusion.

Inclusion Criteria:

- Age between 50 and older

- Diagnosis of mild segmental instability on standing radiography lateral film defined
as degenerative spondylolisthesis ≤ 4mm in dynamic imaging (i.e., flexion/extension)

- Scheduled for an elective single-level posterior decompression and posterolateral
fusion using AspenTM spinous process fixation system

- Oswestry Disability Index (ODI) v 2.1 score >30%

- Failed at least 3 months of conservative care (non-surgical) OR has clinical signs of
neurological deterioration

- Signed Informed Consent Form

Exclusion Criteria:

Pre-operative

- Marked degenerative spondylolisthesis (>4mm)

- Lesions requiring surgery involving two levels

- Prior surgery at index level or adjacent level

- Prior spinal fusion surgery

- Isthmic or lytic spondylolisthesis

- Incompetent or missing posterior arch at the affected level (e.g. complete
laminectomy, pars defect)

- Requires complete laminectomy at level of surgery

- Facet joints at implant level are absent or fractured

- Vertebral body compromise or acute fracture at implant level

- Body mass Index (BMI) ≥ 35

- Known allergy to titanium

- Osteoporosis: SCORE (Simple Calculated Osteoporosis Risk Estimation) will be used to
screen subjects requiring DEXA. Subjects with T-score < -2.5 will be excluded

- Paget's disease, osteomalacia, or any other metabolic bone disease

- Use of medications or any drug known to potentially interfere with bone/soft tissue
healing (e.g. chronic systemic steroids)

- Planned use of additional segmental fixation (eg. facet screws, anterior/lateral
plating, anchored cages)

- Use of Bone Morphogenetic Protein (BMP)*

- Unlikely to comply with the follow-up evaluation schedule

- In the opinion of the Investigator, Subject has history of chemical substance
dependency or significant psychosocial disturbance that may impact the outcome or
study participation

- Active participation in a clinical trial of another drug or device

- Active systemic infection or any other health condition that would preclude surgery

- History of invasive malignancy, except if the subject has received treatment and
displayed no clinical signs and symptoms for at least five years

- Pregnant or planning to become pregnant during study participation

- Involvement in active litigation related to back problems at the time of screening

- Direct involvement in the execution of this protocol

- Pre-existing conditions that could interfere with the evaluation of outcome measures
(e.g. musculoskeletal, neuromuscular, etc.)

Intra-operative Exclusion

- Intra-operative visualization of a > 4mm spondylolisthesis not previously noted
radiographically

- Any change in the surgical procedure that violates the inclusion/exclusion criteria.
(eg. switching to double level procedure; placing pedicle screws as posterior
fixation).