Introduction: Cement pressurisation is key to achieving good cement-bone interdigitation in THR. To obtain adequate pressurisation the medullary canal must be sealed distally using a cement restrictor. The cement restrictor must remain stable in the femoral canal.

Methods: Five different cement restrictors were evaluated, namely the Exeter Cement Plug, Biostop G, Hardinge, Rex CementStop and a preinjected cement plug. The restrictor was deployed in a sawbone that had been reamed to produce a distal flare, based on radiographic measurements. Low viscosity bone cement pressurised using a cement ram connected to a 10bar air supply. An electronic pressure valve increased the pressure in the cement. Cement pressure and cement restrictor displacement were continuously measured. The pressure valve and recording of measurements was controlled by a customised computer package.

Results: The Rex CementStop withstood the greatest pressures (mean 565.8kPa). This was a significantly greater pressure than any of the other cement restrictors (p< 0.001). Pre-injected cement plugs were able to resist the next highest pressures (mean 350.4kPa). They did not displace but leaked cement and were technically difficult to deliver in the distal femur. Cement restrictors that function well above the isthmus were ineffective (Biostop mean 118.7kPa) or could not be deployed below the isthmus (Exeter). The Hardinge recorded a mean 162.3kPa.

Discussion: During pre-operative templating it is important to consider where the cement restrictor will sit in the femur. When the cement restrictor is going to be deployed beyond the femoral isthmus, an alternate method of cement restriction may need to be used. Universal sized plugs (e.g. Hardinge) function poorly in this situation. Press-fit plugs such as Biostop and Exeter are severely compromised when inserted past the femoral isthmus. Pre-injected cement plugs are variable in efficacy. The expandable Rex CementStop reliably occluded the femur, allowing the highest pressures to be generated.

Aims: To evaluate the function of cement restrictors beyond the femoral isthmus.

Introduction: Pressurisation of cement is key to achieving good cement-bone interdigitation in Total Hip Replacement. During insertion of the femoral stem, pressures of up to 1000kPa may be generated. To maintain pressurisation the medullary canal must be sealed distally using a cement restrictor. As a secondary effect, cement restrictors also prevent excess injection of cement into the medullary canal. To fulfil these functions the cement restrictor must remain stable in the femoral canal.

Methods: Five different cement restrictors were evaluated, namely the Exeter Cement Plug (Stryker, UK), Biostop (De Puy, UK), Hardinge (De Puy, UK), Rex CementStop (A-One-Medical, Netherlands) and a preinjected cement plug (Surgical Simplex, Stryker, UK). The restrictor was deployed in a sawbone that had been rasped to produce a distal flare. Low viscosity bone cement (Surgical Simplex, Stryker, UK) was injected and pressurised using a custom made cement ram connected to a 10bar pressurised air supply. An electronically controlled pressure valve increased the pressure in the cement. Pressure in the cement was measured using a pressure transducer. A linear variable displacement transducer was used to measure movement of the cement restrictor. Leakage of cement around the restrictor was also recorded. Activation of the pressure valve and recording of measurements was controlled by a customised computer package.

Results: The Rex CementStop withstood the greatest pressures (mean 565.8kPa). This was a significantly greater pressure than any of the other cement restrictors (p= 0.027). Pre-injected cement plugs were able to resist the next highest pressures (mean 350.4kPa). They did not displace but leaked cement and were technically difficult to deliver in the distal femur. Cement restrictors that function well above the isthmus were ineffective (Biostop mean 118.7kPa) or could not be deployed below the isthmus (Exeter). The Hardinge cement restrictor recorded a mean 162.3kPa.

Discussion: It is important for a surgeon to consider where the cement restrictor will sit in the femur during pre-operative templating in Total Hip Replacement. When the cement restrictor is going to be deployed beyond the femoral isthmus, an alternate method of cement restriction may need to be used. Universal sized plugs (e.g. Hardinge) function poorly in this situation. Press-fit plugs such as Biostop and Exeter have been previously shown to allow the generation of high pressures in bone cement when sited above the femoral isthmus or in stove pipe femurs. However their function is severely compromised when inserted past the femoral isthmus. Pre-injected cement plugs are variable in efficacy. The expandable Rex CementStop was simple to use and reliably occluded the femur, allowing the highest pressures to be generated.

Instrumented gait analysis has evolved into a widely used tool to define and describe abnormalities of gait. It is used as a tool to enhance the performance in sports as well as to measure the effects of conservative or surgical treatment methods. Patients usually walk very slow during gait training, whereas normal data are obtained at regular walking velocity. This may lead to misinterpretations. The purpose of this study was to determine the effects of walking slow towards gait and to establish normal data for “walking slow” on a treadmill.

10 healthy volunteers with no known gait problem underwent training to accommodate to the conditions of treadmill walking. There were 5 females and 5 males. The mean age was 30 [range 22–56] years. Instrumented gait analysis was performed using a camera system (Motion Analysis Systems). Data obtained were processed by OrthotracTM and the proprietary software of our lab. During data acquisition participants were asked to walk at leisure velocity, then they were asked to slow down as much as possible.

The normal walking velocity of was 0,99 [range 0,78–1,16] m/s. When asked to walk as slow as possible the walking speed decreased to 0,29 [range 0,14–0,50] m/s. We noted a change in the ratio between swing and stance periods with less swing time, as well as a increase of double limb support time. Step length decreased. Changes in the pattern of motion included delayed and increased peak ankle dorsiflexion and decrease of ankle plantar flexion at initial contact. 3-D motion data for hip and knee also demonstrate noteworthy changes, generally resulting in a decrease of joint excursion.

Interpretation of gait data obtained from slow walking patients should consider the effects walking velocity. Locomotion therapy (e.g. for spinal cord injuries) should not force patients into motion patterns that are only found at faster walking velocities.