Study Evaluating the Safety and Effectiveness of the FLEXUS(TM) Interspinous Spacer

Absence of implant-related complications, including device dislodgement, defined as: * Failure of implant material (e.g. fracture); * Implant migration outside of the interspinous space (posteriorly beyond the posterior margin of the spinous processes, anteriorly within the spinal canal, or laterally more than half of the implant width); or * Other complications that can be specifically associated with the implanted device.

Time frame: 24 months

Population: The Overall Number of Participants Analyzed in the FLEXUS arm and X-STOP arm is the number of subjects who started the Study in the respective arms. No data was collected for the No Treatment arm.

Neurological status is based on four types of measurement parameters: motor, sensory, reflexes, and special assessments. Each parameter will be coded as follows: Motor 0 Total Paralysis 1. Palpable or Visible Contraction 2. Active Movement, Gravity Eliminated 3. Active Movement, Against Gravity 4. Active Movement, Against Some Resistance 5. Active Movement, Against Full Resistance Sensory 0 Absent 1. Impaired 2. Normal Reflexes 0 Absent or Trace 1. Hyper-reflexic 2. Normal or hypo-reflexic Straight Leg Raise 0 0°-70° (abnormal) 1 \>70°-90° (normal) If all evaluations for the parameter are determined to be normal, then the parameter is given a normal status. If any evaluations for the parameter are abnormal, then the parameter is given an abnormal status. The overall neurological status will be considered a success if and only if all the four parameters are stable or improved.

Time frame: 24 months

Population: The Overall Number of Participants Analyzed is not consistent with numbers in the Participant Flow module. The discrepancy is due to two less subjects having neurologic status data at 24 months in the FLEXUS arm and one less subject with neurologic status data at 24 months in the X-STOP arm. No data was collected for the No Treatment arm.

Change in the Zurich Claudication Questionnaire (ZCQ) score at 24 months compared with the score at baseline as follows: * Change of \>0.5 points in Physical Function on a scale of 1-4 points (lower values are considered a better outcome) * Change of \>0.5 points in Symptom Severity on a scale of 1-5 points (lower values are considered a better outcome) * Satisfaction of \<2.5 points on a scale of 1-4 points (lower values are considered a better outcome) The Zurich Claudication Questionnaire is a three part form that quantifies severity of symptoms, physical function characteristics, and patient's satisfaction after treatment.

Time frame: 24 months

Population: The Overall Number of Participants Analyzed is not consistent with numbers provided in the Participant Flow module. The discrepancy in the numbers is due to an additional subject having ZCQ data at 24 months in the FLEXUS arm and one less subject with ZCQ data at 24 months in the X-STOP group. No data was collected for the No Treatment arm.

Measures the number of participants who did not have another surgery for treatment of lumbar spinal stenosis at the same spinal level that was originally treated. Data, including adverse events, were monitored, evaluated and assessed for evidence of additional surgical treatment at the spinal level that was originally treated.

Time frame: 24 months

Population: The Overall Number of Participants Analyzed in the FLEXUS arm and X-STOP arm is the number of subjects who started the Study in the respective arm. No data was collected for the No Treatment arm.

Change in mental or physical composite score of the short form SF36

Time frame: 24 months

Population: The short form SF36 was administered to study patients; however, we do not have the proprietary scoring system. Hence the scores could not be calculated.

The Oswestry Disability Index (ODI) questionnaire contains ten topics concerning intensity of pain, lifting, ability to care for oneself, ability to walk, ability to sit, sexual function, ability to stand, social life, sleep quality, and ability to travel. Each topic is followed by 6 statements describing different potential scenarios in the patient's life relating to the topic. The subject chooses the statement which most closely resembles their situation. Each question is scored on a scale of 0-5 with the first statement being zero and indicating the least amount of disability and the last statement is scored 5 indicating most severe disability. Scores for all questions answered are summed, then multiplied by two to obtain the index (range 0 to 100). Zero is equated with no disability and 100 is the maximum disability.

Time frame: 24 months

Population: The Overall Number of Participants Analyzed is not consistent with numbers in the Participant Flow module. The discrepancy is due to ten less subjects having ODI data at 24 months in the FLEXUS arm and four less subject with ODI data at 24 months in the X-STOP arm. No data was collected for the No Treatment arm.

The visual analog scale (VAS) is a questionnaire used to quantify a subjective experience, such as the intensity of pain. The scale is a 100mm line labeled with no pain on the left border and as severe as it could be on the right border. The subject is instructed to make a mark along the line to represent the intensity of back pain currently being experienced; 0mm is equal to no pain and 100mm is pain as severe as it could be. The clinician records the distance of the mark in millimeters from the left end of the scale.

Time frame: 24 months

Population: The Overall Number of Participants Analyzed is not consistent with numbers in the Participant Flow module. The discrepancy is due to ten less subjects having ODI data at 24 months in the FLEXUS arm and four less subject with ODI data at 24 months in the X-STOP arm. No data was collected for the No Treatment arm.

The visual analog scale (VAS) is a questionnaire used to quantify a subjective experience, such as the intensity of pain. The scale is a 100mm line labeled with no pain on the left border and as severe as it could be on the right border. The subject is instructed to make a mark along the line to represent the intensity of left leg pain currently being experienced; 0mm is equal to no pain and 100mm is pain as severe as it could be. The clinician records the distance of the mark in millimeters from the left end of the scale.

Time frame: 24 months

Population: The Overall Number of Participants Analyzed is not consistent with numbers in the Participant Flow module. The discrepancy is due to eleven less subjects having VAS data at 24 months in the FLEXUS arm and four less subject with VAS data at 24 months in the X-STOP arm. No data was collected for the No Treatment arm.

The visual analog scale (VAS) is a questionnaire used to quantify a subjective experience, such as the intensity of pain. The scale is a 100mm line labeled with no pain on the left border and as severe as it could be on the right border. The subject is instructed to make a mark along the line to represent the intensity of right leg pain currently being experienced; 0mm is equal to no pain and 100mm is pain as severe as it could be. The clinician records the distance of the mark in millimeters from the left end of the scale.

Time frame: 24 months

Population: The Overall Number of Participants Analyzed is not consistent with numbers in the Participant Flow module. The discrepancy is due to eleven less subjects having VAS data at 24 months in the FLEXUS arm and four less subject with VAS data at 24 months in the X-STOP arm. No data was collected for the No Treatment arm.