Impaction procedure influences primary stability of acetabular press-fit components

Automatic Impactors in Total Hip Arthroplasty: A State-of-the-Art Review

BACKGROUND

Total hip arthroplasty (THA) is an increasingly common procedure that places considerable physical strain on orthopaedic surgeons over time. The procedure requires precise impaction for optimal implant fixation and long-term stability. Automated impactors have emerged as innovative tools to address the limitations of manual mallets, with efforts to improve surgeons' physical health, surgical efficiency, and patient outcomes. This review evaluates the specifications, clinical applications, ergonomic benefits, and occupational hazards such as noise of commercially available automated impactors, including KINCISE, Woodpecker, HAMMR, and orthodrive. This is compared to existing literature on the devices and supplemented with independent noise measurements. It aimed to provide actionable insights to guide device selection based on clinical scenarios and operating room needs.

METHODS

A systematic PubMed search (2013 to 2024) identified 147 relevant articles after excluding studies on impaction grafting and trauma. Product specifications and noise data were supplemented with patent information and manufacturer details. Noise mitigation strategies and ergonomic considerations were also explored. Sound levels of three of the discussed impactors were measured to supplement this review.

RESULTS

Automated impactors demonstrated significant reductions in femoral broaching time, improved consistency, and reduced surgeon fatigue compared to manual methods. Periprosthetic fracture risk was equal to or less than that of manual broaching. Each impactor exhibited unique strengths: KINCISE offered versatility, Woodpecker precision, HAMMR adjustability, and orthodrive the lowest noise production of the devices measured. However, trade-offs compared to the traditional mallet included cost, learning curves, and limited versatility in some devices. Time-weighted average (TWA) noise levels ranged from 57.37 to 67.47 dBA across devices, with maximum levels ranging from 101.2 to 107.3 dBA, remaining below the Occupational Safety and Health Administration TWA 85 dBA threshold and the World Health Organization (WHO) maximum threshold of 110 dBA.

CONCLUSIONS

Automated impactors enhance procedural efficiency and ergonomics in THA, but device selection should be tailored to specific surgical and institutional needs. Noise levels were similar across devices, though close to the WHO maximum threshold. Future research should focus on long-term patient outcomes and standardizing testing protocols for these devices.

Vibratory and conventional impaction of acetabular components into porcine acetabula

Aims

Sufficient primary implant stability with minimal bone damage is one of the challenges for uncemented implant fixation to prevent periprosthetic fractures and implant loosening. A pilot study on a non-viscoelastic material (polyurethane foam) showed a reduced impaction force when using vibratory implant insertion. This study assessed the effectiveness of vibratory implant insertion compared to an established implant insertion method in physiological viscoelastic bone from porcine hips.

Methods

Acetabular components were impacted line-to-line and into 1 mm nominal undersized cavities in porcine acetabula (n = 24 in total, n = 6 acetabula per group of study) using vibration (60 Hz) and 1 Hz (established) impaction methods. The impaction force, remaining polar gap, and lever-out moment were measured and compared between the impaction methods and different press-fits.

Results

The vibratory impaction method produced almost 40% lower impaction forces at both press-fit levels. However, complete seating at the nominal press-fit of 1 mm was not achieved, and primary stability was lower for the vibratory impaction for either press-fit.

Conclusion

Bone fracture risk due to high impaction forces could be reduced by vibrational implant insertion at the cost of a reduction in primary stability. The outcome of the vibratory impaction method in porcine bone was similar to a previous study using polyurethane foams, suggesting that the viscoelasticity of bone may not play a crucial role during press-fit implant impaction.

Use of an Automated Surgical Impactor Reduces Femoral Broaching Time in Direct Anterior Approach Total Hip Arthroplasty: Results From a Randomized, Multicenter Study

Background

Impaction in total hip arthroplasty has typically been conducted using a mallet. A surgical automated impactor has been developed with the goal of reducing surgeon variability, fatigue, and injury. There is also potential to reduce the variability of each impaction step in which automated impaction is used, through reproducible and consistent application of force.

Methods

Patients were randomized into either the mallet control group, or the automated impaction study group (1:1 randomization). The primary endpoint analysis was conducted to demonstrate that femoral broaching time (in minutes) with an automated impactor is noninferior to femoral broaching time with manual instruments (mallet) under a noninferiority (NI) margin of 1.25 minutes, with a subsequent test of superiority. A total of 218 patients were randomized and treated (109 in each group).

Results

Mean femoral broaching time was 5.8 minutes in the automated impaction study group (automated), and 8.1 minutes in the mallet control group (mallet), a 28.4% reduction (P = .0005). However, there was not a difference in surgery duration between the groups. Three fractures were reported in the mallet group and 1 in the automated group.

Conclusions

In this randomized multicenter study, an automated impactor was shown to reduce femoral broaching time in primary total hip arthroplasty, with no increase in fractures, but no decrease in operating room time was noted.

Vibratory insertion of press-fit acetabular components requires less force than a single blow technique

Aims

Periprosthetic fracture and implant loosening are two of the major reasons for revision surgery of cementless implants. Optimal implant fixation with minimal bone damage is challenging in this procedure. This pilot study investigates whether vibratory implant insertion is gentler compared to consecutive single blows for acetabular component implantation in a surrogate polyurethane (PU) model.

Methods

Acetabular components (cups) were implanted into 1 mm nominal under-sized cavities in PU foams (15 and 30 per cubic foot (PCF)) using a vibratory implant insertion device and an automated impaction device for single blows. The impaction force, remaining polar gap, and lever-out moment were measured and compared between the impaction methods.

Results

Impaction force was reduced by 89% and 53% for vibratory insertion in 15 and 30 PCF foams, respectively. Both methods positioned the component with polar gaps under 2 mm in 15 PCF foam. However, in 30 PCF foam, the vibratory insertion resulted in a clinically undesirable polar gap of over 2 mm. A higher lever-out moment was achieved with the consecutive single blow insertion by 42% in 15 PCF and 2.7 times higher in 30 PCF foam.

Conclusion

Vibratory implant insertion may lower periprosthetic fracture risk by reducing impaction forces, particularly in low-quality bone. Achieving implant seating using vibratory insertion requires adjustment of the nominal press-fit, especially in denser bone. Further preclinical testing on real bone tissue is necessary to assess whether its viscoelasticity in combination with an adjusted press-fit can compensate for the reduced primary stability after vibratory insertion observed in this study.

Dynamics of manual impaction instruments during total hip arthroplasty

Aims

Manual impaction, with a mallet and introducer, remains the standard method of installing cementless acetabular cups during total hip arthroplasty (THA). This study aims to quantify the accuracy and precision of manual impaction strikes during the seating of an acetabular component. This understanding aims to help improve impaction surgical techniques and inform the development of future technologies.

Methods

Posterior approach THAs were carried out on three cadavers by an expert orthopaedic surgeon. An instrumented mallet and introducer were used to insert cementless acetabular cups. The motion of the mallet, relative to the introducer, was analyzed for a total of 110 strikes split into low-, medium-, and high-effort strikes. Three parameters were extracted from these data: strike vector, strike offset, and mallet face alignment.

Results

The force vector of the mallet strike, relative to the introducer axis, was misaligned by an average of 18.1°, resulting in an average wasted strike energy of 6.1%. Furthermore, the mean strike offset was 19.8 mm from the centre of the introducer axis and the mallet face, relative to the introducer strike face, was misaligned by a mean angle of 15.2° from the introducer strike face.

Conclusion

The direction of the impact vector in manual impaction lacks both accuracy and precision. There is an opportunity to improve this through more advanced impaction instruments or surgical training.