Introduction. We previously reported a 28% short-term corrosion-related revision rate of recalled Rejuvenate modular stem. The purpose of this study was to assess the mid-term clinical results and survivorship of this implant. Methods. Between June 2009 and July 2012, 73 total hip arthroplasty (THA) in 63 patients with the Rejuvenate modular neck implant were performed by a single surgeon and prospectively followed. Average age was 63.2 ± 12.6 years (28 to 86). Elevated metal ion (= 2 µg/L), pain, or positive MRI findings were indication for revision surgery. Correlation between patient factors with serum metal ion levels and revisions were analyzed. Results. At an average follow-up of 4.2 ± 0.6 years (3.0 to 5.5), 57 hips (48 patients, 78%) were revised at mean of 3.2 ± 1 years (1 to 5.5); and 6 other have been scheduled for surgery. The Kaplan-Meier survivorship was 22 % at 5.5 years. Visible corrosion was seen at the trunion-stem junction in each revision case. 51 of 57 hips undergoing revision (89%), had elevated preoperative serum Co levels, 24 (42%) had elevated preoperative Cr. The average serum Co and Cr ion levels prior to revision surgery were 10 ± 8 µg/L (0.3 to 40) and 2.3 ± 1.5 µg/L (1 to 7.4), respectively. There was a significant correlation between revision surgery and younger age (p=0.0137). 52 hips underwent MRI evaluation, 22 hips (42%) had positive findings correlated to pain (p=0.025): 11 hips demonstrated adverse local soft tissue reactions such as fluid collection, capsular thickening, osteolysis, or synovitis, and 11 hips showed evidence of pseudotumor. Conclusions. At mid-term follow-up, 86% of the Rejuvenated modular neck stems have been revised or awaiting revision. Given these findings, all patients with a Rejuvenate modular neck stem implant should be followed closely and advised of impending failure

Background:. The Rejuvenate modular neck stem (Stryker, Mahwah, NJ) was recently recalled due to corrosion at the neck-stem junction. The purpose of this study was to investigate the rate of corrosion related failures and survivorship of this implant, and analyze the correlation between the implant and patient factors with serum metal ion levels. Material and Methods:. Between June 2009 and July 2012, 123 Rejuvenate stems (97 modular and 26 non-modular) THAs were implanted in 104 patients by a single surgeon via a modified anterolateral approach. Serum Cobalt (Co) and Chromium (Cr) levels (microgram per liter [μg/L]) were obtained in all patients. In cases of elevated serum metal ion levels or symptomatic hip, patients underwent magnetic resonance imaging (MRI) for assessment of osteolysis or adverse local tissue reactions (ALTR). Correlation between implant factors (implant size, head size, head length, offset), patient factors (age, gender, BMI) with serum metal ion levels and revisions were analyzed using logistic regression models. Results:. The mean follow-up was 2.7 ± 0.6 years. The mean Co and Cr levels were 5.4 ± 5.7 μg/L (0.2–31) and 2.1 ± 1.5 μg/L (0.1–4.3), respectively. The differences between the Co and Cr levels in the two groups were statistically significant. 49% of THAs in the modular group had elevated metal ion levels (> 4.0 μg/L). There was a significant correlation between higher metal ion levels, younger age, and higher offset (p < 0.05). Presence of pain and high cobalt levels were significant predictors for revision surgery. The rate of revision at the time of this study was 26%, the majority were in the 2. nd. year after surgery. The Kaplan-Meier survivorship was 75% at the time of this study. Discussion and Conclusions:. The short-term high rate of corrosion related revision with Rejuvenate modular neck stems is extremely alarming. We anticipate more revisions in the near future. Level of Evidence: Level III, Therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence

Lesions in the joint surface are commonly treated with osteoarticular autograft transfer system (OATS), autologous cell implantation (ACI/MACI), or microfracture. Tissue formed buy the latter commonly results in mechanically inferior fibrocartilage that fails to integrate with the surrounding native cartilage, rather than durable hyaline cartilage. Fractional laser treatment to make sub-millimeter (<500 µm) channels has been employed for tissue regeneration in the skin to facilitate rejuvenation without typical scarring. Additionally, we have pioneered a means to generate articular cartilage matrix from chondrocytes—dynamic Self-Regenerating Cartilage (dSRC). Combining these two approaches by performing fractional laser treatment of the joint cartilage and treating with dSRC is a new paradigm for joint surface restoration. This approach was refined in a series of in vitro experiments and tested in swine knee defects during a 6-month study in 12 swine. dSRC are generated by placing 10. 7. swine knee chondrocytes into sealed 15-mL polypropylene tubes and cultured on a rocker at 40 cycles per minute for 14 days at 37°C. The chondrocytes aggregate and generate new extracellular matrix to form a pellet of dSRC. Channels of approximately 300-500 µm diameter were created by infrared laser ablation in swine cartilage (in vitro) and swine knees (in vivo). The diameter and depth of the ablated channel in the cartilage was controlled by the light delivery parameters (power, spot size, pulse duration) from a fractional 2.94 µm Erbium laser. The specimens were evaluated with histology (H&E, safranin O, toluidine blue) and polarized-sensitive optical coherence tomography for collagen orientation. We can consistently create laser-ablated channels in the swine knee and successfully implant new cartilage from dSRC to generate typical hyaline cartilage in terms of morphology and biochemical properties. The neocartilage integrates with host cartilage in vivo. These findings demonstrate our novel combinatorial approach for articular cartilage rejuvenation

Aims. The decrease in the number of satellite cells (SCs), contributing to myofibre formation and reconstitution, and their proliferative capacity, leads to muscle loss, a condition known as sarcopenia. Resistance training can prevent muscle loss; however, the underlying mechanisms of resistance training effects on SCs are not well understood. We therefore conducted a comprehensive transcriptome analysis of SCs in a mouse model. Methods. We compared the differentially expressed genes of SCs in young mice (eight weeks old), middle-aged (48-week-old) mice with resistance training intervention (MID+ T), and mice without exercise (MID) using next-generation sequencing and bioinformatics. Results. After the bioinformatic analysis, the PI3K-Akt signalling pathway and the regulation of actin cytoskeleton in particular were highlighted among the top ten pathways with the most differentially expressed genes involved in the young/MID and MID+ T/MID groups. The expression of Gng5, Atf2, and Rtor in the PI3K-Akt signalling pathway was higher in the young and MID+ T groups compared with the MID group. Similarly, Limk1, Arhgef12, and Araf in the regulation of the actin cytoskeleton pathway had a similar bias. Moreover, the protein expression profiles of Atf2, Rptor, and Ccnd3 in each group were paralleled with the results of NGS. Conclusion. Our results revealed that age-induced muscle loss might result from age-influenced genes that contribute to muscle development in SCs. After resistance training, age-impaired genes were reactivated, and age-induced genes were depressed. The change fold in these genes in the young/MID mice resembled those in the MID + T/MID group, suggesting that resistance training can rejuvenate the self-renewing ability of SCs by recovering age-influenced genes to prevent sarcopenia. Cite this article: Bone Joint Res 2022;11(2):121–133

Modular total hip arthroplasty (MTHA) stems were introduced in order to provide increased intra-operative flexibility for restoring hip biomechanics, improving stability and potentially reducing revision risk. However, the additional interface at the neck-body junction provides another location for corrosion or mechanical failure of the stem. To delineate the mid term revision risk of MTHA stems, we examined data from the Canadian Joint Replacement Registry (CJRR) at the Canadian Institute for Health Information (CIHI). Kinectiv, Profemur and Rejuvenate modular stems were identified from CJRR records submitted between 2004 and 2014. Revision status was determined by examining the discharge abstract database (DAD) also housed by CIHI, which collects information on all revisions, regardless of whether the procedure was submitted to CJRR. A total of 2446 modular stems were identified with a mean follow up of 4.2 years (range 0 to 10). Their usage peaked in 2012 (the first year of mandatory CJRR form submission for BC, ON and MB), and dropped rapidly thereafter. A total of 155 (6.3%) were revised. This consisted of 5/301 Kinectiv (1.7%), 141/2050 ProFemur (6.9%), and 9/96 Rejuvenate (9.4%) stems. As a group, this falls below the National Institute for Clinical Excellence (NICE) guidelines of 95% survival at 10 years. While MTHA stems were introduced to improve outcomes and reduce revision risk, our findings of a 6.3% revision risk at a mean follow up of 4.2 years does not appear to support this

Modularity of femoral components has been widely accepted at the head neck junction, most commonly combining two unlike metals with only sporadic reporting of compatibility issues and corrosion. The development and introduction of a new and improved modular neck junction (Rejuvenate Modular Femoral component, Stryker Orthopedics) provided the option of fine-tuning leg lengths, offset and stability. The surgical technique did indeed provide the desired endpoints, however, the early recognition of problems with the junction causing corrosion and Adverse Local Soft Tissue Reaction (ALTR) and subsequent revision has led to the product being voluntarily withdrawn from the market. My experience as an early user of this stem is described in this manuscript providing a better early recognition and treatment of this potentially very destructive process. Methods. A retrospective review of one hundred and ninety one Rejuvenate Stems that were implanted between January 2010 and January of 2012. However, after March 2011, this stem was only used on those patients who had a rejuvenate stem on the contralateral side. They were all implanted through a mini posterior incision with the first 82 patients receiving a Tritanium cluster hole cup (Stryker Orthopedics) with between two and three screws. The remaining 109 patients had an ADM (Anatomic Dual Mobility, Stryker Orthopedics). All patients were allowed to bear weight as tolerated and were followed up with Xrays at six weeks and one year. Clinical visits were recorded at 2 weeks and 6 months postop. Additional follow up was scheduled every two years following the first annual visit. Results. One hundred and seventy four of the 191 hips were available for review at the one-year follow-up. Fourteen patients have undergone revision of the hip due to increased pain and formation of an avascular pseudo capsule due to corrosion at the neck stem junction. All patients have demonstrated a black flaky residue at the taper junction and all have had a large, tense effusion with a milky colored fluid. A neo caspsule has formed in all patients that appeared avascular and thickened. Seven of the eight tritanium cups in the revision cases were loose and required revision, while none of the ADM cups were loose. One patient has undergone two revisions since the initial cause of failure was not recognized and she subsequently developed pain within three months following placement of a new modular neck at the initial revision. One patient who underwent revision developed a deep infection and is currently on antibiotics but has not cleared the infection as of this writing. Conclusion. There has been catastrophic early failure of a modular femoral component due to corrosion at the neck stem junction during the very early stages of follow up. An intense reaction appears to begin early on, perhaps contributing to failure of bony ingrowth in certain cup designs but not others. Patients who develop early onset of discomfort progress to a poorly functioning hip that presents with pain, swelling and decreased ROM. These patients need to be assessed with serum ion levels, joint aspiration for infection and ion levels if possible. A MRI with MARS technology is useful in identifying joint fluid and neo caspsule expansion. These patients should be advised on the adverse reaction that can develop and revision of the hip should be expeditiously carried out

Orthographic radiography, a revelation at its inception, has been the orthopaedic standard for a century. It has facilitated osteology and empowered arthroplasty like no other parallel technology. While many new imaging modalities – nuclear scans, computerized axial tomography, magnetic resonance imaging, etc. – have advanced the art even further, plain XRays, quite frankly, remain the standard for identifying patient pathology and evaluating surgical intervention. The enlightened scrutiny of properly obtained and successfully reproduced radiographic images still yields far more information in the daily practice of orthopaedics than its more sophisticated and expensive derivatives. A detailed review of readily available diagnostic information is intended to rejuvenate/resuscitate our most valuable ally in the evolving struggle against arthritic disease

Introduction. Dual modular femoral stems for total hip arthroplasty were initially introduced to optimize joint biomechanics. These implants have been recalled due to fretting and crevice corrosion at the stem-neck interface, ultimately necessitating revision in a significant number of patients. At our institution we had experience with the Rejuvenate (Stryker, Mahwah, NJ) dual modular stem from 2009 until 2011 before it's recall in 2012. This study identifies complications encountered in patients requiring revision of this prosthesis. Methods. We retrospectively identified all patients who had one particular dual modular stem using our registry database. All patients’ charts and imaging was reviewed using our electronic medical records and digital imaging programs. Patients’ age, gender, revision date, intraoperative and postoperative complications, need for subsequent surgery were identified. Results. 118 femoral stems were implanted in 107 patients (61 male & 46 female) with average follow up of over 3 years. 40 stems (34%) were revised in 36 patients with an average time to revision of 2.7 years. Women had a revision rate of 42% versus 28% in men for an odds ratio of 1.5. Complications were also increased overall with a predilection for women. 7 (15%) of revisions required an extended trochanteric osteotomy (ETO), and 5 (12.5%) had greater trochanter (GT) fractures. The most common complication postoperatively was dislocation in 25% of patients, 7 of which required reoperation. One patient had an infection after revision requiring 2-stage revision. Discussion and Conclusion. Dual modular femoral stems are associated with a high early failure rate due to fretting and crevice corrosion. Women in particular are at higher risk for need for revision and have a higher complication rate during and after revision. A significant number of our patients required an ETO or had a GT fracture intraoperatively. Additionally, adverse local tissue reactions (ALTR) are shown to affect the abductor muscles and joint capsule. These two factors likely contribute to the high dislocation rate after revision. Preoperatively counsel patients on the higher complication rate and revision should be carried out carefully to prevent fracture and maximize stability of the hip

Aims

Mesenchymal stem cells (MSCs) are usually cultured in a normoxic atmosphere (21%) in vitro, while the oxygen concentrations in human tissues and organs are 1% to 10% when the cells are transplanted in vivo. However, the impact of hypoxia on MSCs has not been deeply studied, especially its translational application.

PURPOSE:. Wright Medical has a long history of modular neck hip implants but had fracture issues with the original titanium necks. They subsequently changed to chrome cobalt modular necks. Direct contact between these dissimilar metal parts in the modular femoral component brings into consideration the possibility of similar adverse reactions of metal-on-metal articulations that have been previously described in other designs. METHODS:. A retrospective review of 10 patients with Wright Medical chrome cobalt modular necks who were evaluated with chromium and cobalt metal ion levels as well as Metal Artifact Reduction Sequence (MARS) MRI's was performed. Pseudotumors were classified by MRI based on wall thickness, T1/T2 signal, shape, and location and given a corresponding type of I, II, or III. For each patient, symptoms or lack thereof were recorded, and time since surgery noted. RESULTS:. Of 10 patients tested, 9 were symptomatic, and 1 was asymptomatic. The patient that was asymptomatic at last clinical visit at 14 months post-op while symptomatic patients averaged 18 months since initial surgery before symptoms began. Those with metal-poly articulation had an average cobalt level of 1.6, ceramic-ceramic articulation had level of <1, and metal-on-metal had level of 2.9. Five patients had pseudotumor by MRI (2 type I, 1 type II, and 2 type III pseudotumors). CONCLUSION:. It appears that an unintended consequence of changing from titanium to chrome cobalt modular neck may be occurring secondary to corrosion at neck-stem junction. SIGNIFICANCE: This reaction does not appear to be design-specific as these findings are similar to our findings in Stryker Rejuvenate stems. Surgeons evaluating patients with these and other similar stems should be aware of this complication and consider ion testing and MARS MRI

Introduction. Failure of the neck-stem taper in one particular bi-modular primary hip stem due to corrosion and wear of the neck piece has been reported frequently1, and stems were recalled. A specific pattern of material loss on the CoCr neck-piece taper in the areas of highest stresses on the proximal medial male taper was observed in a retrieval study of 27 revised Rejuvenate implants revised after 3 to 38 month time in situ (Stryker, Kalamazoo, MI, USA) (Figure 1). One neck piece exhibited additionally wear marks at the distal end of the flat male neck taper indicating contact with the female taper of the stem. The purpose of this study was to understand the observed failure scenario of bottoming-out by investigating the stem taper morphologies. Materials and Methods. The geometry of taper contact surfaces was determined using a Coordinate Measurement Machine (BHN 805, Mitutoyo, Japan). An algorithm based on the individual unworn areas of the respective taper surfaces was applied to all retrievals. One retrieval is additionally investigated by infinite focus microscopy (G4, Alicona, Austria) in the main wear areas on the neck piece taper, and the bottom, facing each other inside the junction (surfaces of the distal end of the male and the bottom of the female taper). Results. The bottom of the male neck piece taper showed a prominent patch surrounded by a corrosion area (Figure 2), similar to the pattern observed in the proximal taper articulation medial- proximally and lateral-distally (Figure 1). The bottom of the female titanium stem taper did not show material loss to this extent, but only slight scratches. The proximal male taper of the neck piece showed the usual corrosion pattern, with an elevated patch protruding inside the corrosion cavity (Figure 3, left). Contrarily to observations on other retrievals (Figure 3, right), the height of this patch did not reach the original surface level. The wear depth at the patch of the bottomed out taper was 93µm with wear reaching as deep as 170µm. Discussion. Only one of 27 retrieved neck pieces showed bottoming out. It can be speculated that the other retrievals were revised before this situation could occur. In the assembled situation, the initial space between the bottom faces of the stem taper is expectedly in the order of a few 100µm. During the observed wear process, permanent contact at patches on the neck piece prevents its reseating, until these localized structures give in to mechanical and electrochemical exposure. This end stage of failure only occurring in one explant indicates high clinical risks of the implants during earlier stages of intact patches, that are usually observed in retrievals. The formation of such patches has not been reported before, and might be characteristic for the wear and corrosion mechanism of the employed TMZF-CoCr combination, possibly due to the reduced stiffness of the TMZF Titanium. Acknowledgements. The research received funding from the European Union's Seventh Framework Program (FP7/2007-2013) under grant agreement GA-310477 (LifelongJoints)

Aims

Ageing-related incompetence becomes a major hurdle for the clinical translation of adult stem cells in the treatment of osteoarthritis (OA). This study aims to investigate the effect of stepwise preconditioning on cellular behaviours in human mesenchymal stem cells (hMSCs) from ageing patients, and to verify their therapeutic effect in an OA animal model.

Having previously been a proponent of the advantages of the modular neck in total hip arthroplasty, I now take the opposite argument because of corrosion that happens with all taper junctions. The advantage of the modular neck is the “uncoupling” of femoral stem position from the final position of the femoral head. Surgical priorities frequently compete, whether positioning the stem for the best press-fit (for cementless fixation) or the best cement mantle (for cemented fixation), and positioning of the stem for preventing dislocation and improving function. My personal use of the modular neck spanned approximately 4 years from 2003–2008 and encompassed a total of 390 primary and revision cases. Excellent functional results were obtained, but some problems occurred that were associated with the modular neck and with large diameter head metal-metal articulations. The modular neck was designed and studied at the Rizzoli Institute in Bologna, Italy with the conclusion that the strength of construct (titanium alloy neck in the titanium alloy stem) was sufficient and the potential for fretting at the modular junction was small and acceptable. Pre-market testing of the device met and exceeded all FDA suggested benchmarks. The first modular neck fracture in my personal series occurred more than 3 years after implantation, in a large man with a long, varus modular neck. Within a year another fracture of a long, varus modular neck occurred in a heavy man. I now know of 6 modular neck fractures among the 390 cases. We have found evidence of corrosion, some very severe, in modular necks that we have revised (both fractured and intact modular necks). This corrosion is caused by Mechanically Assisted Crevice Corrosion associated with fretting at the modular junction which leads to removal of the titanium oxide “passivation” layer that generally forms on a titanium implant. This exposes more of the substrate metal to oxidation and can create pits that, in the notch-sensitive titanium alloy, can lead to the initiation of fracture. The hydrogen that is created from the corrosion reaction and diffused into the metal can cause “embrittlement” which predisposes it to fracture. We also have seen “hydrogen pneumarthrosis” associated with corrosion of the titanium modular neck in which the corrosion concentrated the hydrogen gas in the femoral stem below the modular neck and suddenly was released into the joint with significant pain. The hydrogen gas is irritating to the joint capsule and the patient presents with intense pain and gas in the joint, a clinical picture that can be confused with infection in the joint with a gas-forming organism. We now know that the condition is self-limiting, but suggests that revision of the modular neck construct would be a reasonable course of action. Recently cobalt chromium modular necks have replaced those made of titanium alloy. Since cobalt-chromium is harder and stiffer, the milieu of the taper junction will be different than that of the titanium-titanium junction, and it has been suggested that this will allow safe and long-term use of the modular neck. The first titanium alloy necks were introduced in the early 1990s and it took until the mid-2000s to recognise problems. Last year the Stryker modular neck used with the Rejuvenate stem was recalled because of significant reaction associated with corrosion at the neck-to-stem junction. Corrosion is inevitable at modular junctions exposed to cyclic loading, especially in the milieu of body fluids. We now know that ALTR occurs in response to taper junction corrosion as well, and the more modular junctions there are in a total hip construct, the more debris and potential reaction likely. Fixed neck stems provide satisfactory long-term fixation and function for patients, so despite a functional advantage to the modular neck, it is “a bridge too far”

Tendon is a bradytrophic and hypovascular tissue, hence, healing remains a major challenge. The molecular key events involved in successful repair have to be unravelled to develop novel strategies that reduce the risk of unfavourable outcomes such as non-healing, adhesion formation, and scarring. This review will consider the diverse pathophysiological features of tendon-derived cells that lead to failed healing, including misrouted differentiation (e.g. de- or transdifferentiation) and premature cell senescence, as well as the loss of functional progenitors. Many of these features can be attributed to disturbed cell-extracellular matrix (ECM) or unbalanced soluble mediators involving not only resident tendon cells, but also the cross-talk with immigrating immune cell populations. Unrestrained post-traumatic inflammation could hinder successful healing. Pro-angiogenic mediators trigger hypervascularization and lead to persistence of an immature repair tissue, which does not provide sufficient mechano-competence. Tendon repair tissue needs to achieve an ECM composition, structure, strength, and stiffness that resembles the undamaged highly hierarchically ordered tendon ECM. Adequate mechano-sensation and -transduction by tendon cells orchestrate ECM synthesis, stabilization by cross-linking, and remodelling as a prerequisite for the adaptation to the increased mechanical challenges during healing. Lastly, this review will discuss, from the cell biological point of view, possible optimization strategies for augmenting Achilles tendon (AT) healing outcomes, including adapted mechanostimulation and novel approaches by restraining neoangiogenesis, modifying stem cell niche parameters, tissue engineering, the modulation of the inflammatory cells, and the application of stimulatory factors.

Cite this article: Bone Joint Res 2022;11(8):561–574.

A balanced inflammatory response is important for successful fracture healing. The response of osteoporotic fracture healing is deranged and an altered inflammatory response can be one underlying cause. The objectives of this review were to compare the inflammatory responses between normal and osteoporotic fractures and to examine the potential effects on different healing outcomes. A systematic literature search was conducted with relevant keywords in PubMed, Embase, and Web of Science independently. Original preclinical studies and clinical studies involving the investigation of inflammatory response in fracture healing in ovariectomized (OVX) animals or osteoporotic/elderly patients with available full text and written in English were included. In total, 14 articles were selected. Various inflammatory factors were reported; of those tumour necrosis factor-α (TNF-α) and interleukin (IL)-6 are two commonly studied markers. Preclinical studies showed that OVX animals generally demonstrated higher systemic inflammatory response and poorer healing outcomes compared to normal controls (SHAM). However, it is inconclusive if the local inflammatory response is higher or lower in OVX animals. As for clinical studies, they mainly examine the temporal changes of the inflammatory stage or perform comparison between osteoporotic/fragility fracture patients and normal subjects without fracture. Our review of these studies emphasizes the lack of understanding that inflammation plays in the altered fracture healing response of osteoporotic/elderly patients. Taken together, it is clear that additional studies, preclinical and clinical, are required to dissect the regulatory role of inflammatory response in osteoporotic fracture healing.

Cite this article: Bone Joint Res 2020;9(7):368–385.

Objectives

The use of ceramic femoral heads in total hip arthroplasty (THA) has increased due to their proven low bearing wear characteristics. Ceramic femoral heads are also thought to reduce wear and corrosion at the head-stem junction with titanium (Ti) stems when compared with metal heads. We sought to evaluate taper damage of ceramic compared with metal heads when paired with cobalt chromium (CoCr) alloy stems in a single stem design.

Objectives

We sought to determine if a durable bilayer implant composed of trabecular metal with autologous periosteum on top would be suitable to reconstitute large osteochondral defects. This design would allow for secure implant fixation, subsequent integration and remodeling.

The June 2014 Hip & Pelvis Roundup³⁶⁰ looks at: Modular femoral necks: early signs are not good; is corrosion to blame for modular neck failures; metal-on-metal is not quite a closed book; no excess failures in fixation of displaced femoral neck fractures; noise no problem in hip replacement; heterotopic ossification after hip arthroscopy: are NSAIDs the answer?; thrombotic and bleeding events surprisingly low in total joint replacement; and the elephant in the room: complications and surgical volume.